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Academic Commons Search Resultsen-usBiostratigraphy, paleomagnetism and sedimentology of Late Cenozoic sediments in northwestern Hokkaido, Japanhttp://academiccommons.columbia.edu/catalog/ac:176875
Ujiie, Hiroshi; Saito, Tsunemasa; Kent, Dennis V.; Thompson, Peter R.; Okada, Hakuyu; Klein, George deVries; Koizumi, Itaru; Harper, Jr., Howard E.; Sato, Tomindohttp://dx.doi.org/10.7916/D83N21PNFri, 29 Aug 2014 00:00:00 +0000Four Neogene sedimentary basins in northwestern Hokkaido (latitudes 44°-45° N.), the northernmost island of Japan, were studied to establish a combined microfossil-paleomagnetic sedimentologic stratigraphy. The measured section near Atsuta encompasses a shoaling depositional sequence from upper bathyal depths in the lower part to stagnant, nearshore conditions near the top of the sequence. Magnetostratigraphic evidence and age-diagnostic diatoms indicate the section to be Late Miocene age covering the interval from early Epoch 5 through Epoch 6, and possibly to late Epoch 7. The second measured section located north of Shosanbetsu exposes sediments derived from a volcano-clastic source and deposited on a continental slope with oversteepened slopes. Rich diatom floras from the sequence are assignable to the Denticula seminae var. fossilis-D. kamtschatica and D. kamtschatica Zones. A magnetic signature containing one reversal was observed in the upper part of the section, although the data seem to indicate the lower section to be dominantly normally magnetized. In the northwest Pacific deep-sea sequences, the zonal boundary of these two diatom zones lies between the Nunivak ( = "b") and "c" Events of the Gilbert Epoch, thus the distinct magnetic reversal observed in the upper part of the sequence is correlated with the top of the Nunivak Event. Neogene strata developed near Wakkanai City, the northwestern tip of Hokkaido, appear to have been deposited during a time interval of predominantly reversed geomagnetic polarity. Diatom floras suggest a correlation of these strata with the Denticula kamtschatica Zone which in turn corresponds, in the northwest Pacific deep-sea sequences, to the lower Gilbert Series below a horizon midway between the Nunivak and "c" Events. Diatom rich sediments of the Shimo-Ebekorobetsu area belong to the Yuchi Formation and comprise two assemblages assignable to the D. kamtschatica Zone and the superjacent Denticula seminae var.fossilis-D. kamtschatica Zone. From northern Honshu through Hokkaido to Sakhalin, in the western Pacific coastal region, beds containing the large pecten Fortipecten takahashii (YOKOYAMA) constitute a marker horizon useful for inter-regional correlation. In its southern range of distribution, F. takahashii is a diagnostic species in the lower part of the Tatsunokuchi Formation from which diatom floras assignable to the D. seminae var. fossilis-D. kamtschatica Zone are described. The F. takahashii bed occurs in the Shosanbetsu section, lying within the same diatom zone as the Tastunokuchi Formation and is in a reversely magnetized interval above the Nunivak Event (3.9 m.y. B.P.). The Neogene marine sediments of northwestern Hokkaido were deposited in the back-arc basin and reveal evidence of active arc magmatism at the time of deposition. In this tectonically active back-arc region, sediment-collecting basins shifted from area to area, accumulating sediments only for a relatively short period of time when spurts of active subsidence occurred in a given sedimentary basin.Sedimentary geology, Marine geology, Paleontologydvk2Lamont-Doherty Earth ObservatoryArticlesLeg 68: Introduction, Explanatory Notes, and Conventionshttp://academiccommons.columbia.edu/catalog/ac:176333
Prell, W. L.; Gardner, J. V.; Kent, Dennis V.http://dx.doi.org/10.7916/D8Z899MPThu, 07 Aug 2014 00:00:00 +0000The sixty-eighth cruise of Glomar Challenger was devoted to using the newly developed Hydraulic Piston Corer (HPC) to recover undisturbed, continuous sequences of unlithified sediment. We returned to the vicinities of two rotary-drilled sites (83 and 154). The stratigraphy of these sites indicated that uninterrupted sections of late Neogene and Quaternary sediment should exist at these locations. The ship left Curacao, Dutch Antilles, on 13 August 1979, cored for 11 days at Site 502, and transited from the Caribbean through the Panama Canal. Site 503, in the eastern equatorial Pacific, was cored for seven days, and we then finally transited to Salinas, Ecuador. The results of this cruise (reported in this volume) include preliminary descriptions, based primarily on shipboard observations and analyses, of the material recovered (site chapters) and additional studies performed ashore after the cruise, either by scientists who participated in the cruise or by other invited investigators. The main purpose of this volume is to present not an exhaustive study of the sediment recovered but rather a description, as detailed as possible, of the material recovered on Leg 68 accompanied by interpretations and conclusions that remain preliminary.Marine geology, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryReportsCoseismic sediment deformation during the 1989 Loma Prieta earthquakehttp://academiccommons.columbia.edu/catalog/ac:171912
Borja, Ronaldo I.; Sun, WaiChinghttp://dx.doi.org/10.7916/D87P8WFQWed, 19 Mar 2014 00:00:00 +0000Inelastic horizontal sediment deformation from the MS 7.1, 17 October 1989 Loma Prieta earthquake has been estimated to be on the order of 20 cm at a site in Gilroy, California, about 32 km east of the epicenter. This estimate was based on combined deterministic-stochastic simulations using ground motion data and sediment properties measured from in situ seismic tests and laboratory tests on cored sediment samples of up to 170 m deep. The calculated deformation is comparable to measured horizontal coseismic displacements at various stations in the Santa Cruz network, suggesting that previously back-figured fault rupture mechanisms may have been influenced by the coseismic sediment deformation.Geophysics, Sedimentary geologyws2414Civil Engineering and Engineering MechanicsArticlesMajor Dust Events in Europe during Marine Isotope Stage 5 (130–74 ka): a Climatic Interpretation of the "Markers"http://academiccommons.columbia.edu/catalog/ac:169477
Rousseau, Denis-Didier; Ghil, M.; Kukla, G.; Sima, A.; Antoine, P.; Fuchs, M.; Hatté, C.; Lagroix, F.; Debret, M.; Moine, O.http://dx.doi.org/10.7916/D8XS5SCPFri, 24 Jan 2014 00:00:00 +0000At present, major dust storms are occurring at mid-latitudes in the Middle East and Asia, as well as at low latitudes in Northern Africa and in Australia. Western Europe, though, does not experience such dramatic climate events, except for some African dust reaching it from the Sahara. This modern situation is of particular interest, in the context of future climate projections, since the present interglacial is usually interpreted, in this context, as an analog of the warm Eemian interval. European terrestrial records show, however, major dust events during the penultimate interglacial and early glacial. These events are easily observed in loess records by their whitish-color deposits, which lie above and below dark chernozem paleosols in Central European records of Marine Isotope Stage (MIS) 5 age. We describe here the base of the Dolni Vestonice (DV) loess sequence, Czech Republic, as the reference of such records. The dust is deposited during intervals that are characterized by poor vegetation – manifested by high δ13C values and low magnetic susceptibility – while the fine sand and clay in the deposits shows grain sizes that are clearly different from the overlying pleniglacial loess deposits. Some of these dust events have been previously described as "Markers" or Marker Silts (MS) by one of us (G. Kukla), and are dated at about 111–109 ka and 93–92 ka, with a third and last one slightly visible at about 75–73 ka. Other events correspond to the loess material of Kukla's cycles, and are described as eolian silts (ES); they are observed in the same DV sequence and are dated at about 106–105 ka, 88–86 ka, and 78.5–77 ka. These dates are determined by considering the OSL ages with their errors measured on the studied sequence, and the comparison with Greenland ice-core and European speleothem chronologies. The fine eolian deposits mentioned above, MS as well as ES, correspond to short events that lasted about 2 ka; they are synchronous with re-advances of the polar front over the North Atlantic, as observed in marine sediment cores. These deposits also correlate with important changes observed in European vegetation. Some ES and MS events appear to be coeval with significant dust peaks recorded in the Greenland ice cores, while others are not. This decoupling between the European eolian and Greenland dust depositions is of considerable interest, as it differs from the fully glacial situation, in which the Eurasian loess sedimentation mimics the Greenland dust record. Previous field observations supported an interpretation of MS events as caused by continental dust storms. We show here, by a comparison with speleothems of the same age found in the northern Alps, that different atmospheric-circulation modes seem to be responsible for the two categories of dust events, MS vs. ES.Paleoclimate science, Climate change, Sedimentary geologydr34Lamont-Doherty Earth ObservatoryArticlesThe Magnitude, Timing and Abruptness of Changes in North African Dust Deposition over the Last 20,000 yrhttp://academiccommons.columbia.edu/catalog/ac:168951
McGee, D.; deMenocal, Peter B.; Winckler, Gisela; Stuut, J. B. W.; Bradtmiller, L. I.http://dx.doi.org/10.7916/D8C53HT8Wed, 22 Jan 2014 00:00:00 +0000Reconstructions of eolian dust accumulation in northwest African margin sediments provide important continuous records of past changes in atmospheric circulation and aridity in the region. Existing records indicate dramatic changes in North African dust emissions over the last 20 ka, but the limited spatial extent of these records and the lack of high-resolution flux data do not allow us to determine whether changes in dust deposition occurred with similar timing, magnitude and abruptness throughout northwest Africa. Here we present new records from a meridional transect of cores stretching from 31°N to 19°N along the northwest African margin. By combining grain size endmember modeling with 230Th-normalized fluxes for the first time, we are able to document spatial and temporal changes in dust deposition under the North African dust plume throughout the last 20 ka. Our results provide quantitative estimates of the magnitude of dust flux changes associated with Heinrich Stadial 1, the Younger Dryas, and the African Humid Period (AHP; ∼11.7–5 ka), offering robust targets for model-based estimates of the climatic and biogeochemical impacts of past changes in North African dust emissions. Our data suggest that dust fluxes between 8 and 6 ka were a factor of ∼5 lower than average fluxes during the last 2 ka. Using a simple model to estimate the effects of bioturbation on dust input signals, we find that our data are consistent with abrupt, synchronous changes in dust fluxes in all cores at the beginning and end of the AHP. The mean ages of these transitions are 11.8±0.2 ka (1σ) and 4.9±0.2 ka, respectively.Atmospheric sciences, Biogeochemistry, Sedimentary geologypbd1, gw2002Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesEvidence for abundant isolated magnetic nanoparticles at the Paleocene–Eocene boundaryhttp://academiccommons.columbia.edu/catalog/ac:168042
Wang, Huapei; Kent, Dennis V.; Jackson, Michael J.http://dx.doi.org/10.7916/D84M92HFFri, 06 Dec 2013 00:00:00 +0000New rock magnetic results (thermal fluctuation tomography, high-resolution first-order reversal curves and low temperature measurements) for samples from the Paleocene–Eocene thermal maximum and carbon isotope excursion in cored sections at Ancora and Wilson Lake on the Atlantic Coastal Plain of New Jersey indicate the presence of predominantly isolated, near-equidimensional single-domain magnetic particles rather than the chain patterns observed in a cultured magnetotactic bacteria sample or magnetofossils in extracts. The various published results can be reconciled with the recognition that chain magnetosomes tend to be preferentially extracted in the magnetic separation process but, as we show, may represent only a small fraction of the overall magnetic assemblage that accounts for the greatly enhanced magnetization of the carbon isotope excursion sediment but whose origin is thus unclear.Geology, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesOnlap, Offlap, and the Origin of Unconformity-Bounded Depositional Sequenceshttp://academiccommons.columbia.edu/catalog/ac:164763
Christie-Blick, Nicholashttp://hdl.handle.net/10022/AC:P:21497Thu, 29 Aug 2013 00:00:00 +0000Unconformity-bounded depositional sequences represent the fundamental building blocks of sedimentary successions. They are typically characterized by onlap at the base and by offlap at the top, and they tend to be markedly asymmetrical, with onlap accounting for a larger part of any cycle of sedimentation than offlap. Offlap cannot be attributed solely to erosional truncation, but instead implies that sequence boundaries develop over a finite interval of time. Depositional sequences are commonly associated with a cyclic arrangement of facies, but transgressive-regressive cycles are out of phase with respect to sequence boundaries, which in down-dip locations are both overlain and underlain by progradational deposits, and hence form during times of regression of the shoreline. These observations are used to develop some ideas about the origin of unconformity-bounded sequences, with reference to the inter-related roles of changes in depositional base level and sediment supply. In particular, it is shown than onlap and offlap are due to lateral migration of a “line of critical bypassing”, defined so as to incorporate the effects of sediment loading and compaction as well as the rate of change of elevation with respect to sea level. Downward shifts in onlap may be achieved by either an increase in the rate of eustatic fall or a decrease in the rate of tectonic subsidence, and it is premature to assume that eustatic and tectonic controls on sea level may be distinguished solely on the basis of the frequency of depositional cyclicity. Small shifts in the position of onlap can also be produced by changes in sediment supply, and more attention needs to be paid to the influence of sediment supply in the development of minor boundaries. Unconformities related to eustatic fluctuations are thought to correspond approximately to times of relatively rapid sea-level fall (inflection points), but questions remain about the existence of possible leads and lags of up to View the MathML source cycle, and hence about the degree to which sequence boundaries of eustatic origin may vary in age both within a given basin and from one basin to another.Marine geology, Plate tectonics, Sedimentary geologync11Earth and Environmental SciencesArticlesSequence Stratigraphyhttp://academiccommons.columbia.edu/catalog/ac:164760
Christie-Blick, Nicholas; Driscoll, Neal W.http://hdl.handle.net/10022/AC:P:21497Thu, 29 Aug 2013 00:00:00 +0000Sequence stratigraphy is the study of sediments and sedimentary rocks in terms of repetitively arranged facies and associated stratal geometry (Vail 1987; Van Wagoner et al 1988, 1990; Christie-Blick 1991). It is a technique that can be traced back to the work of Sloss et al ( 1949), Sloss ( 1950, 1963), and Wheeler ( 1958) on interregional unconformities of the North American craton, but it became systematized only after the advent of seismic stratigraphy, the stratigraphic interpretation of seismic reflection profiles (Vail et al 1977, 1984, 1991; Berg and Woolverton 1985; Cross and Lessenger 1988; Sloss 1988; Christie-Blick et al 1990; Van Wagoner et a11990; Vail 1992). Sequence stratigraphy makes use of the fact that sedimentary successions are pervaded by physical discontinuities. These are present at a great range of scales and they arise in a number of quite different ways: for example, by fluvial incision and subaerial erosion (above sea level); submergence of nonmarine or shallow-marine sediments during transgression (flooding surfaces and drowning unconformities), in some cases with shoreface erosion (ravinement); shoreface erosion during regression; erosion in the marine environment as a result of storms, currents, or mass-wasting; and through condensation under conditions of diminished sediment supply (intervals of sediment starvation), The main attribute shared by virtually all of these discontinuities, independent of origin and scale, is that to a first approximation they separate older deposits from younger ones. The recognition of discontinuities is therefore useful because they allow sedimentary successions to be divided into geometrical units that have time-stratigraphic and hence genetic significance.Marine geology, Plate tectonics, Sedimentary geologync11, nwd1Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesDeformation and Basin Formation along Strike-Slip Faultshttp://academiccommons.columbia.edu/catalog/ac:164769
Christie-Blick, Nicholas; Biddle, Kevin T.http://hdl.handle.net/10022/AC:P:21499Thu, 29 Aug 2013 00:00:00 +0000Significant advances during the decade 1975 to 1985 in understanding the geology of basins along strike-slip faults include the following: (1) paleomagnetic and other evidence for very large magnitude strike slip in some orogenic belts; (2) abundant paleo-magnetic evidence for the pervasive rotation of blocks about vertical axes within broad intracontinental transform boundaries; (3) greater appreciation for the wide range of structural styles along strike-slip faults; (4) new models for the evolution of strike-slip basins; and (5) a body of new geophysical and geological data for specific basins. In the light of this work, and as an introduction to the remainder of the volume, the purpose of this paper is to summarize the major characteristics of and controls on structural patterns along strike-slip faults, the processes and tectonic settings of basin formation, and distinctive stratigraphic characteristics of strike-slip basins. Strike-slip faults are characterized by a linear or curvilinear principal displacement zone in map view, and in profile, by a subvertical fault zone that ranges from braided to upward-diverging within the sedimentary cover. Many strike-slip faults, even those involving crystalline basement rocks, may be detached within the middle to upper crust. Two prominent characteristics are the occurrence of en echelon faults and folds, within or adjacent to the principal displacement zone, and the co-existence of faults with normal and reverse separation. The main controls on the development of structural patterns along strike-slip faults are (1) the degree to which adjacent blocks either converge or diverge during strike slip; (2) the magnitude of displacement; (3) the material properties of the sediments and rocks being deformed; and (4) the configuration of pre-existing structures. Each of these tends to vary spatially, and, except for the last, to change through time. It is therefore not surprising that structural patterns along strike-slip faults differ in detail from simple predictions based on the instantaneous deformation of homogeneous materials. In the analysis of structural style, it is important to attempt to separate structures of different ages, and especially to distinguish structures due to strike-slip deformation from those predating or post-dating that deformation. Distinctive aspects of structural style for strike-slip deformation on a regional scale include evidence for simultaneous shortening and extension, and for random directions of vergence in associated thrusts and nappes. Sedimentary basins form along strike-slip faults as a result of localized crustal extension, and, especially in zones of continental convergence, of localized crustal shortening and flexural loading. A given basin may alternately experience both extension and shortening through variations in the motion of adjacent crustal blocks, or extension in one direction (or in one part of the basin) may be accompanied by shortening in another direction (or in another part of the basin). The directions of extension and shortening also tend to vary within a given basin, and to change through time; and the magnitude of extension may be depth-dependent. Theoretical studies and observations from basins where strike-slip deformation has ceased suggest that many strike-slip basins experience very little thermally driven post-rift subsidence. Strike-slip basins are typically narrow (less than about 50 km wide), and they rapidly lose anomalous heat by accentuated lateral as well as vertical conduction. Detached or thin-skinned basins also tend to be cooler after rifting has ended than those resulting from the same amount of extension of the entire lithosphere. In some cases, subsidence may be arrested or its record destroyed as a result of subsequent deformation. Subsidence due to extension, thermal contraction, or crustal loads is amplified by sediment loading. The location of depositional sites is determined by (1) crustal type and the configuration of pre-existing crustal structures; (2) variations in the motion of lithospheric plates; and (3) the kinematic behavior of crustal blocks. The manner in which overall plate motion is accommodated by discrete slip on major faults, and by the rotation and internal deformation of blocks between those faults is especially important. Subsidence history cannot be determined with confidence from present fault geometry, which therefore provides a poor basis for basin classification. Every basin is unique, and palinspastic reconstructions are useful even if difficult to undertake. Distinctive aspects of the stratigraphic record along strike-slip faults include (1) geological mismatches within and at the boundaries of basins; (2) a tendency for longitudinal as well as lateral basin asymmetry, owing to the migration of depocenters with time; (3) evidence for episodic rapid subsidence, recorded by thick stratigraphic sections, and in some marine basins by rapid deepening; (4) the occurrence of abrupt lateral facies changes and local unconformities; and (5) marked differences in stratigraphic thickness, facies geometry, and occurrences of unconformities from one basin to another in the same region.Geology, Plate tectonics, Sedimentary geologync11Earth and Environmental SciencesArticlesIs There a Role for Sequence Stratigraphy in Chronostratigraphy?http://academiccommons.columbia.edu/catalog/ac:164645
Christie-Blick, Nicholas; Pekar, Stephen F.; Madof, Andrew S.http://hdl.handle.net/10022/AC:P:21459Wed, 28 Aug 2013 00:00:00 +0000Sequence stratigraphy revolutionized the field of stratigraphy in the late 1970s and 1980s by providing an interpretive depositional framework for integrating diverse stratigraphic data at the scale of sedimentary basins. However, a lack of consensus on criteria for recognizing, mapping and hence dating sequence boundaries, interpretations of uneven quality, and doubts about the universal eustatic origin and global synchrony of unconformity-related sequences limit the usefulness of sequence stratigraphy in chronostratigraphy.Sedimentary geology, Geologync11, sfp32, asm2124Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesRegional Structure and Kinematic History of the Sevier Fold-and-Thrust Belt, Central Utah: Discussionhttp://academiccommons.columbia.edu/catalog/ac:164648
Christie-Blick, Nicholas; Anders, Mark H.http://hdl.handle.net/10022/AC:P:21460Wed, 28 Aug 2013 00:00:00 +0000DeCelles and Coogan (2006) summarize the structure and evolution of the Late Jurassic to Paleocene Sevier orogenic belt in central Utah, inferring at least 220 km of crustal shortening on the basis of a regional balanced cross section. Difficulties arise in an otherwise excellent synthesis in their treatment of the Sevier Desert basin, where 47 km of normal slip is interpreted on a Cenozoic detachment in spite of mounting evidence that no such structure exists. DeCelles and Coogan acknowledge the possibility that the prominent seismic reflection marking the Paleozoic-Cenozoic contact may correspond with an unconformity rather than a fault. However, they dismiss the inconvenient absence of evidence for deformation along the interpreted detachment as “local and equivocal,” ignore a comprehensive re-evaluation of subsurface geophysical and geological data by Wills et al. (2005), and claim incorrectly that the construction of a balanced cross section “implicitly demonstrates the geometric and kinematic validity of the detachment interpretation for the …. reflection” (p. 844). Balanced cross sections are only as good as the observational constraints and assumptions upon which they are based. If the detachment that is a central assumption of DeCelles and Coogan's cross section is, in fact, not a fault, a better section can be drawn.Geology, Geomorphology, Sedimentary geologync11, mha1Earth and Environmental SciencesArticlesSpatial Variations in a Condensed Interval between Estuarine and Open-Marine Settings: Holocene Hudson River Estuary and Adjacent Continental Shelfhttp://academiccommons.columbia.edu/catalog/ac:164676
McHugh, Cecilia M.; Pekar, Stephen F.; Christie-Blick, Nicholas; Ryan, William B. F.; Carbotte, Suzanne M.; Bell, Robin E.http://hdl.handle.net/10022/AC:P:21469Wed, 28 Aug 2013 00:00:00 +0000An interval of stratigraphic condensation extending for 300 km from the fluvially dominated Hudson River estuary to the adjacent continental shelf reveals stratal relationships within an unconformity-related depositional sequence that are commonly difficult to resolve in seismic reflection profiles and outcrop. High-resolution side-scan sonar and bathymetry, more than 100 sediment cores ∼2 m long, and radioisotope (14C, 137Cs) age control show that much of the valley was filled by ca. 3 to 1 ka. The present rate of sediment accumulation averages 1 mm/yr, corresponding with a sea-level rise of ∼1.2 mm/yr relative to local bedrock. Condensation is manifested today by sedimentary bypass in most parts of the estuary and by the trapping of available sediment (1.2–5.6 × 105 t/yr [metric tons]) along narrow reaches and primarily in the vicinity of the estuarine turbidity maximum, a part of the estuary located upstream of the salinity intrusion ∼25 km from the mouth (3.0 × 105 t/yr). Shelf condensation is due to sediment starvation. The condensed interval merges updip with a nascent sequence boundary as the estuary reaches its final filling phase and downdip with the sequence boundary that developed at the Last Glacial Maximum. Delta progradation may take place as available shelf accommodation is filled, but such sediments are expected to be removed once sea level begins to fall. This sedimentation pattern, in which a condensed interval merges with different sequence boundaries, is consistent with the stratigraphic record of the Atlantic margin back to the Paleogene and may be typical of sediment-starved margins.Sedimentary geology, Remote sensing, Marine geologycmm4, sfp32, nc11, wbr1, smc29, reb4Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesStable Isotope Record of the Terminal Neoproterozoic Krol Platform in the Lesser Himalayas of Northern Indiahttp://academiccommons.columbia.edu/catalog/ac:164654
Kaufman, Alan J.; Jiang, Ganqing; Christie-Blick, Nicholas; Banerjee, Dhiraj M.; Rai, Vibhutihttp://hdl.handle.net/10022/AC:P:21462Wed, 28 Aug 2013 00:00:00 +0000The terminal Neoproterozoic succession in the Lesser Himalaya of India, including the Infra Krol Formation and Krol Group, represent the thickest known accumulation of carbonate strata of this time period, and hence is an ideal target for chemostratigraphic and sequence stratigraphic investigation. High-resolution analyses reveal several negative δ13C excursions. Only one of these is related to known Neoproterozoic ice ages, and many vary in amplitude and stratigraphic position in an oblique regional transect of the platform. A combination of stratigraphic and geochemical tests, and comparison with sections elsewhere, leads to an evaluation of the relative contributions of primary and secondary signals. Two excursions are associated with abrupt facies changes associated with shallowing and accumulation of carbonate in organic-rich restricted environments, or with karstification of a subaerially exposed platform; these are currently interpreted to be diagenetic artifacts. Other negative δ13C excursions are recorded in open marine transgressive facies, and are interpreted to represent biogeochemical anomalies of global significance. The magnitude of these excursions, however, is complicated by their lateral inconsistency between adjacent sections. Two interpretations are proposed. One possibility is that the observed isotopic inconsistency is due to diagenesis not revealed by the application of existing geochemical criteria. A composite δ13C curve constructed under this assumption is broadly consistent with that documented elsewhere, and may reflect modest biogeochemical changes of global scale. An alternative interpretation is that the inconsistency of δ13C values relates to stratigraphic hiatus between correlated horizons, incomplete sampling, and/or lack of appropriate carbonates facies. The composite δ13C curve constructed under this assumption shows large-magnitude (up to 15‰) negative δ13C anomalies that are taken to imply remarkable perturbations of ocean geochemistry and the episodic input of 13C-depleted alkalinity during terminal Neoproterozoic time.Sedimentary geology, Geochemistry, Paleoclimate sciencenc11Earth and Environmental SciencesArticlesStratigraphy, Sedimentary Structures, and Textures of the Late Neoproterozoic Doushantuo Cap Carbonate in South Chinahttp://academiccommons.columbia.edu/catalog/ac:164657
Jiang, Ganqing; Kennedy, Martin J.; Christie-Blick, Nicholas; Wu, Huaichun; Zhang, Shihonghttp://hdl.handle.net/10022/AC:P:21463Wed, 28 Aug 2013 00:00:00 +0000The 3- to 5-m-thick Doushantuo cap carbonate in south China overlies the glaciogenic Nantuo Formation (ca. 635 Ma) and consists of laterally persistent, thinly laminated and normally graded dolomite and limestone indicative of relatively deep-water deposition, most likely below storm wave base. The basal portion of this carbonate contains a distinctive suite of closely associated tepee-like structures, stromatactis-like cavities, layer-parallel sheet cracks, and cemented breccias. The cores of tepees are composed of stacked cavities lined by cements and brecciated host dolomicrite. Onlap by laminated sediment indicates synsedimentary disruption of bedding that resulted in a positive seafloor expression. Cavities and sheet cracks contain internal sediments, and they are lined by originally aragonitic isopachous botryoidal cements with acicular radiating needles, now replaced by dolomite and silica. Pyrite and barite are common, and calcite is locally retained as a primary mineral. These features share morphological and petrographic attributes with modern and ancient methane seeps in which methane gas and fluids provide both a force for physical disruption from buoyancy and a source of alkalinity for significant cementation. The presence of δ13C values as low as −41‰ in well preserved limestone crusts and cements within and immediately above the tepee-like structures provides unequivocal evidence for methane influence, and the widespread distribution of identical sedimentary structures and paragenetic cement sequences across the entire basin at the same basal cap carbonate level is consistent with gas hydrate destabilization and the development of methane seeps as a result of postglacial warming of the ocean. Considering the broad distribution of similar features at the same stratigraphic level in other cap carbonates globally, we suggest that the late Neoproterozoic postglacial methane release may have influenced the oceanic oxygen level as well as contributed to postglacial warming via the greenhouse effects of methane.Geology, Marine geology, Sedimentary geologync11Earth and Environmental SciencesArticlesQuantitative Constraints on the Origin of Stratigraphic Architecture at Passive Continental Margins: Oligocene Sedimentation in New Jersey, U.S.A.http://academiccommons.columbia.edu/catalog/ac:164691
Pekar, Stephen F.; Christie-Blick, Nicholas; Miller, Kenneth G.; Kominz, Michelle A.http://hdl.handle.net/10022/AC:P:21473Wed, 28 Aug 2013 00:00:00 +0000The Oligocene of the New Jersey continental margin is divisible into as many as eight sequences and 23 lithofacies associations, documented in a series of seven boreholes across the modern coastal plain. This paper summarizes the sequence architecture of these deposits, interpreted from high-resolution biostratigraphy and Sr-isotope chemostratigraphy, and evaluates the factors that governed patterns of sedimentation, making use of previously published quantitative estimates of water-depth changes and eustasy from 2-D foraminiferal paleoslope modeling and flexural backstripping. Each sequence is markedly wedge-shaped, thinning both landward of the rollover in the underlying sequence boundary (the point at which the surface steepens into a clinoform), and seaward of the rollover in the overlying boundary. Each bounding surface is associated with evidence for offlap-onlap geometry and at least locally with benthic foraminiferal evidence for abrupt upward shoaling. Most unconformities merge up dip into a single surface marking the Oligocene-Miocene boundary. Earliest Oligocene unconformities (33.5-31.6 Ma) merge downdip as a result of sediment starvation on the deep shelf. Conventional lithostratigraphic units within the New Jersey Oligocene are highly diachronous. For example, the base of Atlantic City Formation at Cape May (a downdip borehole) is at least 6.6 Myr younger than the top of the same formation at ACGS#4 (an updip borehole). Factors controlling patterns of sedimentation include: (1) a terraced physiography, with gradients ranging from 1:1,000 (0.06°) on the coastal plain and shallow shelf and 1:500 (0.11°) on the deep shelf to less than 1:100 (1.0°) on an intermediate slope; (2) generally low siliciclastic sediment flux, with in situ production of authigenic glauconite, especially during times of transgression; (3) a location landward of the hinge zone of the passive margin, with slow tectonic subsidence augmented by compaction and sediment loading; (4) low to moderate amplitudes and rates of eustatic change (10-50 m over spans of ∼ 1-2 Myr); and (5) an active wave climate that permitted efficient lateral transport and complete bypass of sediment at paleodepths of at least 20 ± 10 m. Sequence architecture in the New Jersey Oligocene differs from that of the standard "Exxon model." Sequences are highstand-dominated, in spite of deposition and preservation largely seaward of the rollover in each underlying sequence boundary. Transgressive systems tracts are thin. Recognizable lowstand units did not form because efficient transfer of sediment across the shallow shelf, combined with the absence of major river systems in the area of study, prevented the reorganization of sedimentation patterns commonly associated with point-source development, in spite of rates of eustatic fall considerably greater than the local rate of tectonic subsidence. Repeated eustatic rises and falls are expressed primarily by variations in paleo-water depth. Although ∼ 65-80% of the shallow shelf that had been flooded during each rise became subaerially exposed during the subsequent fall, well developed offlap at each sequence boundary is due primarily to marine bypassing and degradation rather than to "forced regression." Sequence boundaries correspond in time at their correlative conformities not with the onset of falling "relative" sea level, but with the start of eustatic rise.Sedimentary geology, Continental dynamics, Geochemistrysfp32, nc11Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesCarbonate Platform Growth and Cyclicity at a Terminal Proterozoic Passive Margin, Infra Krol Formation and Krol Group, Lesser Himalaya, Indiahttp://academiccommons.columbia.edu/catalog/ac:164694
Jiang, Ganqing; Christie-Blick, Nicholas; Kaufman, Alan J.; Banerjee, Dhiraj M.; Rai, Vibhutihttp://hdl.handle.net/10022/AC:P:21474Wed, 28 Aug 2013 00:00:00 +0000The Infra Krol Formation and overlying Krol Group constitute a thick (less than 2 km), carbonate-rich succession of terminal Proterozoic age that crops out in a series of doubly plunging synclines in the Lesser Himalaya of northern India. The rocks include 18 carbonate and siliciclastic facies, which are grouped into eight facies associations: (1) deep subtidal; (2) shallow subtidal; (3) sand shoal; (4) peritidal carbonate complex; (5) lagoonal; (6) peritidal siliciclastic–carbonate; (7) incised valley fill; and (8) karstic fill. The stromatolite-rich, peritidal complex appears to have occupied a location seaward of a broad lagoon, an arrangement reminiscent of many Phanerozoic and Proterozoic platforms. Growth of this complex was accretionary to progradational, in response to changes in siliciclastic influx from the south-eastern side of the lagoon. Metre-scale cycles tend to be laterally discontinuous, and are interpreted as mainly autogenic. Variations in the number of both sets of cycles and component metre-scale cycles across the platform may result from differential subsidence of the interpreted passive margin. Apparently non-cyclic intervals with shallow-water features may indicate facies migration that was limited compared with the dimensions of facies belts. Correlation of these facies associations in a sequence stratigraphic framework suggests that the Infra Krol Formation and Krol Group represent a north- to north-west-facing platform with a morphology that evolved from a siliciclastic ramp, to carbonate ramp, to peritidal rimmed shelf and, finally, to open shelf. This interpretation differs significantly from the published scheme of a basin centred on the Lesser Himalaya, with virtually the entire Infra Krol–Krol succession representing sedimentation in a persistent tidal-flat environment. This study provides a detailed Neoproterozoic depositional history of northern India from rift basin to passive margin, and predicts that genetically related Neoproterozoic deposits, if they are present in the High Himalaya, are composed mainly of slope/basinal facies characterized by fine-grained siliciclastic and detrital carbonate rocks, lithologically different from those of the Lesser Himalaya.Sedimentary geology, Geology, Geomorphologync11Earth and Environmental SciencesArticlesEvaluating the Stratigraphic Response to Eustasy from Oligocene Strata in New Jerseyhttp://academiccommons.columbia.edu/catalog/ac:164718
Pekar, Stephen F.; Christie-Blick, Nicholas; Kominz, Michelle A.; Miller, Kenneth G.http://hdl.handle.net/10022/AC:P:21482Wed, 28 Aug 2013 00:00:00 +0000Previously published Oligocene eustatic records are compared with observed stratigraphic architecture at the New Jersey continental margin in order to evaluate the stratigraphic response to eustatic change. Lower to mid-Oligocene sequence boundaries (33.8–28.0 Ma) are associated with relatively long hiatuses (0.3–0.6 m.y.), in which sedimentation in many places terminated during eustatic falls and resumed early during eustatic rises. Upper Oligocene sequence boundaries are associated with relatively short hiatuses (less than 0.3 m.y.), and provide the best constraints on phase relations between sea-level forcing and margin response. The interval represented by each upper Oligocene sequence varies in dip profile. At updip locations, landward of the clinoform rollover in the underlying sequence boundary, sedimentation commenced after the eustatic low and terminated before the eustatic high (with partial erosion of any younger record). At downdip locations, sedimentation within each sequence was progressively delayed in a seaward direction, beginning during the eustatic rise and terminating near the eustatic low. Combining data from all available boreholes, ages of sequence boundaries (correlative surfaces) correspond closely with the timing of eustatic lows, and ages of condensed sections (intervals of sediment starvation) correspond with eustatic highs.Geology, Continental dynamics, Sedimentary geologysfp32, nc11Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesLate Miocene to Pleistocene Sequences at the New Jersey Outer Continental Shelf (ODP Leg 174A, Sites 1071 and 1072)http://academiccommons.columbia.edu/catalog/ac:164730
Metzger, J. M.; Flemings, P. B.; Christie-Blick, Nicholas; Mountain, Gregory S.; Austin Jr., J. A.; Hesselbo, S. P.http://hdl.handle.net/10022/AC:P:21487Wed, 28 Aug 2013 00:00:00 +00002-D seismic, wireline log, and core data at ODP Leg 174A Sites 1071 and 1072 on the outer continental shelf of New Jersey reveal two major depositional sequences of late Miocene–Pliocene and Pleistocene age. The late Miocene–Pliocene sequence is a thick (∼100 m) deepening-upward succession landward of the clinoform rollover and a shoaling-upward succession seaward of the clinoform rollover. The Pleistocene sequence deepens abruptly near its base, shoals upward, and then deepens again before it is truncated by its overlying unconformity. There is no onlap onto clinoforms (no lowstand wedge) in either sequence. Sequence stratigraphic analysis and a geometric depositional model are used to interpret that the unusually thick transgressive component of the late Miocene–Pliocene sequence was formed by high-frequency eustatic cycles (1–2 m.y.) superimposed on a longer-term eustatic rise (∼5 m.y.). This conclusion is supported by independent evidence of eustasy. The sequences of this study are correlated to sequences in the North Atlantic coastal plain and in the Great Bahama Bank. These sequences have very different architectures than underlying middle Miocene sequences, which contain thick lowstand wedge deposits, and are interpreted to have formed by high-frequency eustatic cycles superimposed on longer-term eustatic fall.Sedimentary geology, Continental dynamics, Paleoclimate sciencenc11, gsm3Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesNew Sequence Perspective on the Devonian Reef Complex and the Frasnian-Famennian Boundary, Canning Basin, Australiahttp://academiccommons.columbia.edu/catalog/ac:164594
Kennard, John M.; Southgate, Peter N.; Jackson, Michael J.; O'Brien, Phillip E.; Christie-Blick, Nicholas; Holmes, Ann E.; Sarg, J. F.http://hdl.handle.net/10022/AC:P:21442Tue, 27 Aug 2013 00:00:00 +0000The application of concepts of sequence stratigraphy to seismic and well data has led to a new understanding of the subsurface Devonian reef complex of the Canning Basin. It demonstrates marked reciprocal sedimentation with lowstand terrigenous sediments largely restricted to the basin and transgressive and highstand carbonate sediments on the platform. Preliminary outcrop studies indicate the potential of these concepts to modify significantly the existing lithostratigraphic and biostratigraphic interpretations of this classic exhumed reef complex, including the stratigraphic context of the Frasnian-Famennian boundary in the Canning Basin.Geomorphology, Marine geology, Sedimentary geologync11Earth and Environmental SciencesArticlesEvidence for Two Pulses of Glaciation during the Late Proterozoic in Northern Utah and Southeastern Idahohttp://academiccommons.columbia.edu/catalog/ac:164597
Crittenden Jr., Max D.; Christie-Blick, Nicholas; Link, Paul Karlhttp://hdl.handle.net/10022/AC:P:21443Tue, 27 Aug 2013 00:00:00 +0000A record of glaciation during late Proterozoic time is preserved in a number of localities extending from the Sheeprock Mountains, Utah, to Pocatello, Idaho, and from the Park City area 40 km east of Salt Lake City to the Deep Creek Range along the Utah-Nevada line. Over much of this area, the glacial deposits and associated rocks thicken westward and form the basal part of a miogeoclinal wedge that accumulated near the late Proterozoic and early Paleozoic continental margin. In the east, such deposits are thin and rest on Archean basement or rocks of Proterozoic Y age; in the west, they are part of thicker sequences in which deposition apparently continued without significant interruption from late Proterozoic into Cambrian time. In many places, the original continuity between the western and eastern parts of the depositional wedge has been obscured by thrusting of Cretaceous and early Tertiary age that carried the thick basinal sequences eastward over those deposited on the continental platform. Recent mapping of Fremont Island in Great Salt Lake, the Wasatch Range between Ogden and Brigham City, and the Sheeprock Mountains shows that glacial episodes represented either by diamictite or by dropstones enclosed in finegrained laminated beds are separated by as much as 1,000 m of non-glacial deposits, including black slate, alternating graywacke and siltstone, quartzite, and conglomerate. Using reasonable sedimentation rates for such deposits and by comparison with modern analogues, we infer that two episodes of glaciation, each probably consisting of multiple advances and retreats, were separated by a non-glacial interval of a few hundred thousand to a few million years' duration. Correlation of the allochthonous, miogeoclinal glacial deposits with the single glacial unit present in autochthonous and parautochthonous platform sites is uncertain, but our interpretation of sedimentary facies and paleogeography suggests that only the younger of the two episodes recorded in the allochthon is represented by the diamictites of the autochthon.Geomorphology, Geology, Sedimentary geologync11Earth and Environmental SciencesArticlesSequence Stratigraphy in Proterozoic Successionshttp://academiccommons.columbia.edu/catalog/ac:164606
Christie-Blick, Nicholas; Grotzinger, John P.; Von der Borch, C. C.http://hdl.handle.net/10022/AC:P:21446Tue, 27 Aug 2013 00:00:00 +0000Sedimentological logging and facies mapping have been used to identify depositional sequences bounded by subtle but regionally persistent unconformities in rocks of Proterozoic age in the western United States, South Australia, and northwestern Canada. We conclude from these studies that the sequence stratigraphic approach is of considerable importance for intrabasinal time correlation in the Proterozoic and for facies interpretation and basin analysis in Proterozoic rocks.Geology, Sedimentary geology, Mineralogync11Earth and Environmental SciencesArticlesSpectral Analysis of the Lower Eocene Wilkins Peak Member, Green River Formation, Wyoming: Support for Milankovitch Cyclicityhttp://academiccommons.columbia.edu/catalog/ac:164632
Machlus, Malka L.; Olsen, Paul E.; Christie-Blick, Nicholas; Hemming, Sidney R.http://hdl.handle.net/10022/AC:P:21455Tue, 27 Aug 2013 00:00:00 +0000This study is the first to employ spectral analysis to examine meter-scale sedimentary cyclicity in the Wilkins Peak Member of the lower Eocene Green River Formation of Wyoming. Generally regarded as the classic example for orbital forcing of lacustrine sediments at eccentricity and precession time scales, this long-standing interpretation was recently contested, with a much shorter duration (≤ 10 ky) inferred for the dominant cyclicity. Earlier work lacked adequate age control or spectral analysis or both. Our analysis is based upon an evaluation in the frequency domain of oil-yield values from four boreholes, accuracy estimation for suggested orbital interpretations, and comparison to independent geochronology. Cored intervals 266–364 m thick represent a span of 1.2–1.7 m.y., with temporal resolution of ∼ 3–5 ky (∼ 1 m) for oil-yield values. Variations in spectral power with depth within the original records are interpreted to reflect changes in the rate of sediment accumulation. These changes are corrected prior to testing the orbital forcing hypothesis by using two methods: 1) a minimal adjustment (three segments) accounting for the dominant changes of spectral frequency with depth; and 2) correlating the published definitions of precessional cycles in these records to a 21 ky cosine curve. Orbital age models resulting from the two tuning methods are compared to available chronology and the tuned records are tested for the expected spectral peaks from orbitally forced records. We conclude that the dominant cyclicity of the Wilkins Peak Member is orbitally forced. Orbital age models overlap 40Ar/39Ar ages and inferred periods include long and short eccentricity, weak obliquity and precession. Eccentricity is resolved in the analyzed records but the expected ∼ 95 and ∼ 125 ky periods are not resolved, controlling the range of possible tuning periods and the accuracy of orbital age models. Sub-Milankovitch variability exists and can be resolved to a minimum period of ∼ 3–5 ky by the analyzed records. However, it cannot be characterized fully with the available chronology or by the previously calculated mean cycle duration.Remote sensing, Sedimentary geology, Geomorphologymlm64, peo1, nc11, srh17Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesStratigraphic Controls on a Salt-Withdrawal Intraslope Minibasin, North-Central Green Canyon, Gulf of Mexico: Implications for Misinterpreting Sea Level Changehttp://academiccommons.columbia.edu/catalog/ac:164626
Madof, Andrew S.; Christie-Blick, Nicholas; Anders, Mark H.http://hdl.handle.net/10022/AC:P:21453Tue, 27 Aug 2013 00:00:00 +0000Three-dimensional seismic data from the Fuji basin, a salt-controlled intraslope minibasin in north-central Green Canyon, Gulf of Mexico, reveal complex interactions between gravity- and suspension-driven sedimentation. Seismic volumes for late Pleistocene (sim470 ka) to Holocene fill within the Fuji basin consist of approximately 45% mass transport complexes (MTCs), 5% channelized sandy turbidites, and 50% hemipelagites and muddy turbidites. At least ten MTCs within the Fuji basin flowed radially toward its depocenter, either from basin flanks (i.e., intrabasinal) or as a result of larger-scale salt motion (i.e., extrabasinal). Sediment transport directions are inferred on the basis of elongate basal incisions and smaller-scale scours, head scarps, fold orientation within the complexes, and stratigraphic thinning trends at downdip margins. An amalgamated set of three channelized sandy turbidite complexes less than 350 m (1148 ft) thick and 3 km (1.8 mi) across represents the main sand delivery pathway into the Fuji basin. These deposits are thought to be due to shelf bypass, and possibly, to proximity to the Pleistocene shoreline. Hemipelagites and muddy turbidites are homogeneous, and their thickness is relatively consistent at basin scale. This facies represents background sedimentation. A process-driven model has been developed involving halokinetic autocyclicity as the primary control on sedimentation in the Fuji basin. Passive salt motion accounts better for both the directions of sediment transport and the frequency of late Pleistocene–Holocene MTCs than currently popular eustatic and steady-state bathymetric models. The conclusion is significant in casting doubt on the generally assumed importance of eustasy in controlling off-shelf lowstand sedimentation and in implying marked variations in stratigraphic details at length scales of less than 10 km (6.2 mi).Petroleum geology, Marine geology, Sedimentary geologyasm2124, nc11, mha1Earth and Environmental SciencesArticlesRe-Evaluation of the Middle Miocene Eagle Mountain Formation and Its Significance as a Piercing Point for the Interpretation of Extreme Extension Across the Death Valley Region, California, U.S.A.http://academiccommons.columbia.edu/catalog/ac:164629
Renik, Byrdie; Christie-Blick, Nicholas; Troxel, Bennie W.; Wright, Lauren A.; Niemi, Nathan A.http://hdl.handle.net/10022/AC:P:21454Tue, 27 Aug 2013 00:00:00 +0000The Death Valley area of eastern California and southern Nevada has been highly influential in the development of ideas about extreme crustal extension. One of the tightest constraints on Death Valley extension is apparently provided by clasts in inferred alluvial-fan deposits of the Eagle Mountain Formation (~ 15–11 Ma) and their source in the Hunter Mountain batholith, now located more than 100 km from some of the deposits. Because alluvial fans are usually less than 10–20 km in radius, the remaining separation has been interpreted as tectonic. New research reported here suggests that the Eagle Mountain Formation at its type location was deposited in a fluvial–lacustrine setting, and provides no constraint on either the magnitude or the direction of tectonic transport and/or crustal extension. Confidence in palinspastic reconstruction thus depends on resolving ambiguities in the correlation of pre-extensional markers or on the recognition of demonstrably proximal facies tectonically distributed across the region. The succession at Eagle Mountain comprises (1) diffusely stratified monolithologic carbonate breccia and sandstone (~ 140 m) onlapping Cambrian carbonate rocks at an unconformity with ~ 110–140 m of relief (fluvial or fluvially influenced); (2) ~ 10 m of tabular-bedded siltstone, diamictite, and sandstone (lacustrine); (3) cross-stratified and channelized sandstone and polymict conglomerate bearing Hunter Mountain clasts, with minor siltstone and carbonate (~ 110 m; mostly fluvial); and (4) tabular-bedded sandstone, siltstone, and minor carbonate (~ 140 m; mostly lacustrine). Eight prominent stratigraphic discontinuities mapped within the third interval are characterized by up to 15 m of local erosional relief, and by abrupt upward coarsening from siltstone or carbonate to conglomerate or sandstone. A fluvial interpretation for the same critical part of the succession is based upon the existence of the mapped surfaces; the ubiquitous development of channels, trough cross-stratification, and upward fining trends (particularly between the mapped surfaces); and the abundance of well rounded clasts in conglomerate. Paleocurrents are generally directed between southward and eastward, although with considerable dispersion, and they shift from approximately southward or southeastward in the mostly fluvial deposits to approximately eastward in the upper lacustrine interval. An unusual feature of the Eagle Mountain Formation at Eagle Mountain is the presence of five crosscutting conglomerate bodies, interpreted as vertically infilled fissures of tectonic origin. Numerous normal, reversed normal, and oblique-slip faults with up to 34 m of stratigraphic separation are thought to postdate sedimentation and tilting of the Eagle Mountain Formation after ~ 11 Ma.Plate tectonics, Sedimentary geology, Geomorphologybr88, nc11Earth and Environmental SciencesArticlesWorking Hypotheses for the Origin of the Wonoka Canyons (Neoproterozoic), South Australiahttp://academiccommons.columbia.edu/catalog/ac:164538
Christie-Blick, Nicholas; Von der Borch, C. C.; DiBona, P. A.http://hdl.handle.net/10022/AC:P:21426Mon, 26 Aug 2013 00:00:00 +0000Recent attempts to apply concepts of sequence stratigraphy to the Neoproterozoic Wilpena Group of the Adelaide "geosyncline" in South Australia have provided an important new method for improving the resolution of intrabasinal correlation in sparsely fossiliferous and unfossiliferous strata. Eight regional unconformities are now recognized within or bounding the Wilpena Group. The most prominent of these, at or near the base of the Wonoka Formation, is expressed by a series of spectacular incised valleys or canyons, some more than 1 km deep and dated as approx 630 to 580 Ma. The canyons developed following an interval of continental rifting that took place between about 800 and 700 Ma and prior to a second phase of accelerated subsidence of uncertain origin in Early Cambrian time (after about 560 Ma). Subsidence during the intervening span of more than 140 my was in part of thermal origin and in part due to the withdrawal of buried salt at depth, but it may also have involved additional extension for which little direct structural evidence is preserved. The canyons are incised into a succession of shallow marine mainly terrigenous strata that accumulated in a broad north- and east-facing ramp. They are exposed in two distinct belts within and east of the Flinders Ranges, in an area that is about 275 km in a north-south direction and about 175 km east-west. The canyons are inferred to have been filled by shallow marine sediments primarily on the basis of sedimentary structures interpreted as combined flow and oscillation ripples and hummocky cross-stratification. If this is correct, development of the canyons was related to regional lowering of depositional base level by more than 1 km. Recent work also indicates a second phase of valley incision at an unconformity immediately above the main canyons and involving a relative sealevel fall of at least 200 m. Two working hypotheses are advanced to account for the origin of the Wonoka canyons: regional uplift and an evaporitic lowering of sealevel in an isolated basin, analogous to the Messinian event in the Mediterranean. Any regional uplift would likely have been of tectonic origin. Diapirism associated with buried salt cannot account for the wide distribution of erosion or for pronounced uplift in an extensional setting lacking evidence for basin inversion or compressional deformation coeval with sedimentation. One possible mechanism for tectonic uplift involves inhomogeneous extension of the lithosphere, with the amount of extension balanced at all levels on a regional scale possibly by means of detachment faults. Possible difficulties with this hypothesis are the requirement of relatively uniform uplift over distances of hundreds of kilometers and the fact that repeated large-scale lowering of base level implies oscillatory vertical motions that are not readily explained. An evaporitic drawdown accounts for the wide distribution and scale of the canyons and for repeated lowering of base level. Possible difficulties in this case are the presence within the canyon fill of facies that have been interpreted to be of tidal origin; the fact that unlike the Messinian crisis in the Mediterranean, the Wonoka canyons do not appear to have been drowned rapidly; and the lack of direct evidence for evaporities of appropriate age. Neither hypothesis accounts for the apparent absence of appreciable meteoric diagenesis in areas far removea from sites of canyon incision. Two additional conclusions are as follows. First, neither of the hypotheses precludes eustasy as an important control on sedimentation. Sequence stratigraphic comparisons with other basins of the same general age should focus primarily on the time of formation of sequence boundaries not on the geometry of the boundaries or the facies involved. Second, a drawdown in excess of 1 km implies that the adjacent basin was originally at least this deep and hence likely underlain at least locally by highly attenuated continental crust or oceanic crust. Either hypothesis therefore has important implications for the tectonic development of the Adelaide geosyncline.Sedimentary geology, Plate tectonics, Marine geologync11Earth and Environmental SciencesArticlesSequence Stratigraphy and Evolution of a Basin-Slope Succession: The Late Proterozoic Wonoka Formation, Flinders Ranges, South Australiahttp://academiccommons.columbia.edu/catalog/ac:164569
DiBona, P. A.; Von der Borch, C. C.; Christie-Blick, Nicholashttp://hdl.handle.net/10022/AC:P:21435Mon, 26 Aug 2013 00:00:00 +0000A shelf to basin‐slope transition is vertically and laterally exposed within the Late Proterozoic Wonoka Formation in the northern Flinders Ranges of South Australia. The shelf to basin‐slope transition can be divided into four units (C to F) which are defined on the basis of facies, sedimentary structures, contacts, stratal geometry, and the type and abundance of down‐slope mass movement. The lowest unit (C) is mudstone dominated and parallel laminated with rare synsedimentary slides. Unit D, a thin, resedimented siliciclastic‐carbonate unit deposited on a sequence boundary at the end of unit C progradation, displays a lateral facies change from well bedded ‘outer shelf deposits in the east to basin‐slope debris flows in the west. Unit E forms a shallowing and coarsening upward succession from ‘outer shelf siltstone to ‘inner shelf storm wave influenced sandstone deposits. The unit thickens westwards, in the interpreted down‐slope direction, where it becomes finer grained and thinner bedded and displays an increasing abundance of synsedimentary slides. Unit F, deposited on an inferred shelf to basin‐slope transition, coarsens and shallows upward, thickens to the west and contains the highest percentage of sandstone and synsedimentary slides. Unit G, deposited at shelf depths, also shallows and coarsens upward from a thin, basal carbonate‐siliciclastic member, with sandstone increasing upsection to a gradational contact with the Pound Subgroup. Three sequences can be defined within this transition on the basis of facies, stratal terminations, and facies discontinuities at inferred sequence boundaries. Each sequence is marked by a transgressive base, overlain by a shallowing‐upward succession. On the inferred shelf and near the shelfbreak, toward the top of the succession, facies discontinuities at sequence boundaries are more obvious, with distinct contrasts in lithology and inferred palaeoenvironments; farther down‐slope and stratigraphically lower in the succession, the boundaries are cryptic, and only lateral tracing of the contacts from the shelf to the slope or the observation of stratal terminations permits them to be recognized.Geology, Sedimentary geology, Marine geologync11Earth and Environmental SciencesArticlesLate Proterozoic Patsy Springs Canyon, Adelaide Geosyncline: Submarine or Subaerial Origin?http://academiccommons.columbia.edu/catalog/ac:164581
Von der Borch, C. C.; Grady, A. E.; Eickhoff, K. H.; DiBona, P.; Christie-Blick, Nicholashttp://hdl.handle.net/10022/AC:P:21438Mon, 26 Aug 2013 00:00:00 +0000A significant aspect of Late Proterozoic sedimentation in the Adelaide Geosyncline, South Australia, is the presence of kilometre-deep erosional incisions which have been termed canyons. These structures were formerly described to be of submarine origin, cut and filled in an inferred basin-slope setting by subaqueous processes. Subsequent detailed research, particularly on a specific incision known as Patsy Springs Canyon, indicates that sedimentary structures within some of the canyon-filling sediments are indicative of deposition above fair weather wave base. In addition, an unusual carbonate unit, which is observed to veneer upper portions of canyon shoulders and to contribute to carbonate breccias interbedded with canyon-fill, has a stable isotope signature which may imply a non-marine origin. The presence of the carbonate veneer, where it is in situ, suggests that at least upper portions of the canyons could have been emergent during the canyon-filling phase. Considering these observations, and combining them with regional stratigraphical relationships, an alternative model for canyon genesis is proposed involving subaerial erosion and subsequent filling by coastal onlap. Such a model requires base-level changes of the order of 1 km, in order to account for observed canyon cutting and filling. Vertical movements associated with halokinesis, or thermally-induced uplift of the order of 1 km, could have resulted in the observed erosional events. Alternatively, a Messinian-style evaporitic lowering of base-level is currently receiving serious attention. With present knowledge this mechanism most satisfactorily explains all observations.Geochemistry, Marine geology, Sedimentary geologync11Earth and Environmental SciencesArticlesExtension, disruption, and translation of an orogenic wedge by exhumation of large ultrahigh-pressure terranes: Examples from the Norwegian Caledonideshttp://academiccommons.columbia.edu/catalog/ac:162021
Brueckner, Hannes K.; Cuthbert, Simon J.http://hdl.handle.net/10022/AC:P:20638Fri, 07 Jun 2013 00:00:00 +0000Far-traveled allochthons (greater than 100 km) within collisional orogenic wedges may have undergone significant lateral movement by passive transport (in addition to thrusting) where they lie tectonically above large, exhumed, high-pressure/ultrahigh-pressure (HP/UHP) metamorphic terranes. Continental collision results in the subduction of one craton beneath another into the mantle. The subducted craton undergoes HP/UHP metamorphism, while an accretionary orogenic wedge develops simultaneously at its junction with the overlying craton. The subsequent exhumation of a large HP/UHP terrane by either far-field extension or buoyancy-driven extrusion, or both, reverses the shear traction along its upper boundary from foreland-directed thrust motion to hinterland-directed normal displacement. This normal-sense shear can stretch, thin, and fragment the overlying wedge and even carry a detached frontal fragment passively toward the foreland on top of the exhuming plate. The total “piggyback” displacement would be a function of the amount of exhumation of the HP/UHP terrane and the timing of its breakoff from the hinterland portion of the wedge. This model is applied to the Trondheim and Jotun nappe complexes of the Caledonides of southern Scandinavia, which were translated greater than 300 km to the E and SE, respectively, during the 430–385 Ma Scandian orogeny. Their hinterland boundaries rest on top of the HP/UHP Western Gneiss Complex. Kinematic indicators along their basal décollements indicate a change in shear sense from top-E/SE to top-W/NW at the same time (ca. 405 Ma) that radiometric ages indicate the Western Gneiss Complex began to exhume from the mantle. Displacements of tens of kilometers along these décollements stretched and thinned the Trondheim nappe complex and fragmented the Jotun nappe complex. Ultimately, this basal traction led to the breakaway of the frontal segments of the allochthons, allowing them to be carried passively to the E/SE as the Western Gneiss Complex continued to exhume. Top-W/NW shear continued between the Western Gneiss Complex and the stranded rearward segments of the allochthons, resulting in the opening up of the Western Gneiss Region tectonic window between the E/SE-translating nappes and their relatively “fixed” equivalents in the W/NW. The total displacement of the traveled frontal allochthons could have been considerably farther than that accomplished by thrusting alone.Geology, Plate tectonics, Sedimentary geologyhkb2Lamont-Doherty Earth ObservatoryArticlesContourite or turbidite?: magnetic fabric of fine-grained Quaternary sediments, Nova Scotia continental risehttp://academiccommons.columbia.edu/catalog/ac:144304
Shor, Alexander N.; Kent, Dennis V.; Flood, Roger D.Fri, 03 Feb 2012 00:00:00 +0000Samples of three piston cores and one gravity core from the Nova Scotia continental rise (depths 4210-4925 m) have been examined to differentiate parallel-to-slope and downslope depositional processes in Quaternary deposits from a region presently influenced by a strong contour current. Measurement of anisotropy of magnetic susceptibility of samples of a red-brown, silt-laminated lutite 'contourite' facies shows grain alignments which are consistent with both parallel-to-slope (contour current) flow and downslope (turbidity current) flow. We believe that these results provide support for the hypothesis that 'geologically significant' contour currents have influenced continental rise deposition during the Pleistocene. However, our observation that both alongslope and downslope alignments are present in lithologically similar units clearly demonstrates the need for studies on the relationship between lithofacies and process in this geological setting.Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesDetection and correction of inclination shallowing in deep sea sediments using the anisotropy of anhysteretic remanencehttp://academiccommons.columbia.edu/catalog/ac:143992
Collombat, Helene; Rochette, Pierre; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12403Mon, 30 Jan 2012 00:00:00 +0000Paleomagnetic data from recent Pleistocene to recent deep sea sediments from the continental rise of eastern North America exhibit a cyclical inclination shallowing, up to 30Â° with respect to the geocentric axial dipole value. This shallowing is strongly correlated with a ratio of anhysteretic remanent magnetization (ARM) anisotropy determined from a four position ARM anisotropy method. It is therefore proving that inclination variations in these cores are not due to paleosecular variation but in part to a bias in the remanence recording processes linked to depositional anisotropy. This study suggests that ARM anisotropy could provide a method to identify and correct for inclination shallowing in natural sediments.Sedimentary geology, Remote sensingdvk2Lamont-Doherty Earth ObservatoryArticlesPost-depositional Remanent Magnetisation in Deep-sea Sedimenthttp://academiccommons.columbia.edu/catalog/ac:143640
Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12273Fri, 20 Jan 2012 00:00:00 +0000Sediments of various lithologies cored from most parts of the deep ocean floor have been found to contain a record of the past behaviour of the Earth's magnetic field, especially the sequence of reversals over at least the past 5 m.y. (ref. 1). The mechanism by which these sediments acquired their natural remanent magnetism (NRM) is, however, still poorly understood. We have recently conducted experiments that indicate that post-depositional remanent magnetisation (ref. 2) is a viable mechanism of magnetisation of deep-sea sediments.Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesPalaeomagnetic field intensity variation recorded in a Brunhes epoch deep-sea sediment corehttp://academiccommons.columbia.edu/catalog/ac:143558
Kent, Dennis V.; Opdyke, Neil D.http://hdl.handle.net/10022/AC:P:12279Fri, 20 Jan 2012 00:00:00 +0000Deep-sea sediments have been shown to possess a natural remanent magnetisation (NRM) that often can be attributed to the statistical alignment of detrital magnetic grains in the Earth's magnetic field at or shortly after the time of their deposition. In favourable circumstances this remanence can be interpreted as a record of palaeomagnetic field behaviour. In the study reported here we have attempted to describe relative variations in palaeomagnetic field intensity on a time scale of 104-105 yr, during the past 700,000 yr, using the palaeomagnetic record of deep-sea sediment piston core RC10-167 (33°2′N, 150°23′E), which has an exceptionally thick section of sediment deposited during the Brunhes normal polarity epoch (Fig. 1). After subtracting the stratigraphic contribution of several distinct volcanic ash layers interspersed with the otherwise uniform pelagic sediment, we calculate an average deposition rate of 2.1cm kyr-1 between the adjusted level (1,470cm) of the Brunhes-Matuyama boundary (t=700,000 yr) and the top of the core, assumed t=0 yr. A 2-cm thick sample, representing about 1,000 yr of deposition, was taken at an average interval of 3.3 cm (representing about 1,600 yr). This sampling placed a theoretical limit of 3,000-4,000 yr on the period of a resolvable sinusoidal variation.Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesCenozoic Era: Geomagnetic polarity time-scalehttp://academiccommons.columbia.edu/catalog/ac:143523
Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12270Thu, 19 Jan 2012 00:00:00 +0000A new geomagnetic polarity time-scale for the late Cretaceous and Cenozoic (Cande and Kent, 1992: CK92) was based on an analysis of magnetic anomaly profiles from the world's ocean basins. It is the first time since Heirtzler et al. (1968) published their time-scale that the relative widths of the magnetic polarity intervals for this entire interval have been systematically determined from magnetic profiles.Sedimentary geology, Paleontologydvk2Lamont-Doherty Earth ObservatoryArticlesA revised Cenozoic geochronology and chronostratigraphyhttp://academiccommons.columbia.edu/catalog/ac:143520
Berggren, William A.; Kent, Dennis V.; Swisher, Carl C.; Aubry, Marie-Pierrehttp://hdl.handle.net/10022/AC:P:12269Thu, 19 Jan 2012 00:00:00 +0000Since the publication of our previous time scale (Berggren and others, 1985c = BKFV85) a large amount of new magneto- and biostratigraphic data and radioisotopic ages have become available. An evaluation of some of the key magnetobiostratigraphic calibration points used in BKFV85, as suggested by high precision 40Ar/39Ar dating (e.g., Montanari and others, 1988; Swisher and Prothero, 1990; Prothero and Swisher, 1992; Prothero, 1994), has served as a catalyst for us in developing a revised Cenozoic time scale. For the Neogene Period, astrochronologic data (Shackleton and others, 1990; Hilgen, 1991) required re-evaluation of the calibration of the Pliocene and Pleistocene Epochs. The significantly older ages for the Pliocene-Pleistocene Epochs predicted by astronomical calibrations were soon corroborated by high precision 40Ar/39Ar dating (e.g., Baksi and others, 1992; McDougall and others, 1992; Tauxe and others, 1992; Walter and others, 1991; Renne and others, 1993). At the same time, a new and improved definition of the Late Cretaceous and Cenozoic polarity sequence was achieved based on a comprehensive evaluation of global sea-floor magnetic anomaly profiles (Cande and Kent, 1992). This, in turn, led to a revised Cenozoic geomagnetic polarity time scale (GPTS) based on standardization to a model of South Atlantic spreading history (Cande and Kent, 1992/1995 = CK92/95). This paper presents a revised (integrated magnetobiochronologic) Cenozoic time scale (IMBTS) based on an assessment and integration of data from several sources. Biostratigraphic events are correlated to the recently revised global polarity time scale (CK95). The construction of the new GPTS is outlined with emphasis on methodology and newly developed polarity history nomenclature. The radioisotopic calibration points (as well as other relevant data) used to constrain the GPTS are reviewed in their (bio)stratigraphic context. An updated magnetobiostratigraphic (re)assessment of about 150 pre-Pliocene planktonic foraminiferal datum events (including recently available high southern (austral) latitude data) and a new/modified zonal biostratigraphy provides an essentially global biostratigraphic correlation framework. This is complemented by a (re)assessment of nearly 100 calcareous nannofossil datum events. Unrecognized unconformities in the stratigraphic record (and to a lesser extent differences in taxonomic concepts), rather than latitudinal diachrony, is shown to account for discrepancies in magnetobiostratigraphic correlations in many instances, particularly in the Paleogene Period. Claims of diachrony of low amplitude (<2 my) are poorly substantiated, at least in the Paleocene and Eocene Epochs. Finally, we (re)assess the current status of Cenozoic chronostratigraphy and present estimates of the chronology of lower (stage) and higher (system) level units. Although the numerical values of chronostratigraphic units (and their boundaries) have changed in the decade since the previous version of the Cenozoic time scale, the relative duration of these units has remained essentially the same. This is particularly true of the Paleogene Period, where the Paleocene/Eocene and Eocene/Oligocene boundaries have been shifted ~2 my younger and the Cretaceous/Paleogene boundary ~1 my younger. Changes in the Neogene time scale are relatively minor and reflect primarily improved magnetobiostratigraphic calibrations, better understanding of chronostratigraphic and magnetobiostratigraphic relationships, and the introduction of a congruent astronomical/paleomagnetic chronology for the past 6 my (and concomitant adjustments to magnetochron age estimates).Sedimentary geology, Paleontologydvk2Lamont-Doherty Earth ObservatoryArticlesBrunhes-Matuyama Polarity Transition in Three Deep-Sea Sediment Coreshttp://academiccommons.columbia.edu/catalog/ac:143506
Clement, Bradford M.; Kent, Dennis V.; Opdyke, Neil D.http://hdl.handle.net/10022/AC:P:12266Thu, 19 Jan 2012 00:00:00 +0000The Brunhes-Matuyama polarity transition was studied in three deep-sea sediment cores obtained from the mid-northern and equatorial Pacific Ocean. Rates of sedimentation vary from 0.7 to 1.1 cm ka-1. The cores were sampled across the transition in 4 mm slices, and each level was further subdivided into three specimens. Inclinations above and below the transition interval are in close agreement with that of an axial dipole field. Estimates of transition duration based on directional change range from 4900 to 8500 years. The transition can be described by a longitudinally confined portion in each of the v.g.p. paths, but is complicated by broad loops in all three records. While fine-scale sampling reveals considerable detail, the notable increase in within-level dispersion observed in the transition and the apparent differences in v.g.p. paths in nearby cores from the same region indicate that factors other than the geomagnetic field may contribute to these transition records.Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesHydraulic piston coring of late Neogene and Quaternary sections in the Caribbean and equatorial Pacific: Preliminary results of Deep Sea Drilling Project Leg 68http://academiccommons.columbia.edu/catalog/ac:143426
Prell, Warren L.; Gardner, James V.; Adelseck, Charles; Blechschmidt, Gretchen; Fleet, Andrew J.; Keigwin, Lloyd D.; Kent, Dennis V.; Ledbetter, Michael T.; Mann, Ulrich; Mayer, Larry; Reidel, William R.; Sancetta, Constance; Spariosu, Dann J.; Zimmerman, Herman B.http://hdl.handle.net/10022/AC:P:12243Wed, 18 Jan 2012 00:00:00 +0000Leg 68 of the Deep Sea Drilling Project used the newly developed Hydraulic Piston Corer (HPC) to recover two virtually continuous, undisturbed sections of late Neogene and Quaternary sediment. The sites are located in the western Caribbean (Site 502, 4 holes) and in the eastern equatorial Pacific (Site 503, 2 holes). The sediment of Site 502 is primarily foram-bearing nanno marl which accumulated at about 3 to 4 cm/thousand yr. The bottom of Site 502 (228.7 m) is ~8 m.y. old. The sediment of Site 503 is primarily siliceous calcareous ooze which accumulated at about 2 to 3 cm/thousand yr. The bottom of Site 503 (235.0 m) is ~8 m.y. old. The magnetostratigraphy of both sites was determined on the R.V. Glomar Challenger with a long-core spinner magnetometer. All paleomagnetic boundaries through the Gilbert were identified in Site 502; most of them were identified in Site 503. The sediment at both sites shows a distinct cyclicity of calcium carbonate content. These relatively high accumulation rate, continuous, undisturbed HPC cores will enable a wide variety of high-resolution biostratigraphic, paleoclimatic, and paleoceanographic studies heretofore not feasible.Physical oceanography, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesMagnetostratigraphy and paleomagnetic poles from Late Triassic-earliest Jurassic strata of the Newark basinhttp://academiccommons.columbia.edu/catalog/ac:143449
Witte, William K.; Kent, Dennis V.; Olsen, Paul E.http://hdl.handle.net/10022/AC:P:12248Wed, 18 Jan 2012 00:00:00 +0000The Newark basin contains a 7-km-thick sedimentary section, which spans approximately 25 m.y. of the Late Triassic and earliest Jurassic (middle Carnian to Hettangian). Previously paleomagnetic study of the Newark red beds has demonstrated that complete progressive thermal demagnetization can effectively isolate a high-temperature characteristic magnetization. In the lower Newark strata (middle Carnian to early Norian in age), this magnetization yielded a pole position at 54°N, 102°E, and in the upper Newark strata (Hettangian in age) a pole position at 55°N, 95°E. Results from 23 new sites in the middle and upper Norian red beds of the Passaic Formation, including 15 sites from the Jacksonwald region that yield a positive fold test, fill the temporal gap between our two prior studies and yield a pole position at 56°N, 95°E (A95 = 4.4°). These results from the middle Newark confirm that North American apparent polar wander was very slow (~0.2°/m.y.) during the Late Triassic through earliest Jurassic. These new sites define reversed and normal polarity magnetozones that are stratigraphically consistent with and extend our previous results. The Newark reversed and normal polarity characteristic magnetizations form a correlatable pattern of 12 magnetozones that are stratigraphically coherent throughout the basin with respect to independent lithostratigraphic marker units that reflect synchronous, basinwide variations in water depth. Temporal calibration of the Newark magnetostratigraphy on the basis of biostratigraphy, radiometric age determinations, and Milankovich-driven cyclostratigraphy indicates that geomagnetic polarity was reversed 70% of the time and that the mean polarity duration was 2 m.y. or less during the Late Triassic and earliest Jurassic.Physical oceanography, Sedimentary geologydvk2, peo1Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesEocene-Oligocene sea-level changes on the New Jersey coastal plain linked to the deep-sea recordhttp://academiccommons.columbia.edu/catalog/ac:143446
Miller, Kenneth G.; Kent, Dennis V.; Brower, Andrew N.; Bybell, Laurel M.; Feigenson, Mark D.; Olsson, Richard K.; Poore, Richard Z.http://hdl.handle.net/10022/AC:P:12247Wed, 18 Jan 2012 00:00:00 +0000We use magnetostratigraphy and Sr-isotope stratigraphy to improve stratigraphic control for the Eocene to Oligocene of the New Jersey coastal plain (ACGS4 borehole). Magnetostratigraphy in many cases is complicated in outcrop sections of shallow-water (<200 m paleodepth) sediments by low remanence and weathering; we minimize these problems by analyzing large samples obtained from the ACGS4 borehole and construct a firm magnetochronology for the early to middle Eocene. Sr-isotope stratigraphy confirms biostratigraphic evidence for a previously unknown uppermost Eocene to lowermost Oligocene unit and delineates a "middle" Oligocene hiatus that is unresolvabie using biostratigraphy alone. We recognize hiatuses and associated unconformities on the New Jersey margin near the lower Eocene/middle Eocene boundary, within the middle Eocene, and in the "middle" Oligocene and correlate these events with similar hiatuses observed in other continental-shelf, slope, and epicontinental settings. In addition, a hiatus probably occurred near the middle Eocene/upper Eocene boundary. We conclude that the interregional distribution of these Eocene-Oligocene hiatuses indicates a global cause: eustatic change.Physical oceanography, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesHigh-resolution stratigraphy of the Newark rift basin (early Mesozoic, eastern North America)http://academiccommons.columbia.edu/catalog/ac:143462
Olsen, Paul E.; Kent, Dennis V.; Cornet, Bruce; Witte, William K.; Schlische, Roy W.http://hdl.handle.net/10022/AC:P:12252Wed, 18 Jan 2012 00:00:00 +0000Virtually the entire Late Triassic and earliest Jurassic age section of the early Mesozoic Newark continental rift basin has been recovered in over 6770 m of continuous core as part of the Newark Basin Coring Project (NBCP). Core was collected using an offset drilling method at seven sites in the central part of the basin. The cores span most of the fluvial Stockton Formation, all of the lacustrine Lockatong and Passaic formations, the Orange Mountain Basalt, and nearly all of the lacustrine Feltville Formation. The cores allow for the first time the full Triassic-age part of the Newark basin stratigraphic sequence to be described in detail. This includes the gray, purple, and red, mostly fluvial Stockton Formation as well as the 53 members that make up the lacustrine Lockatong (mostly gray and black) and Passaic (mostly red) formations. The nearly 25% overlap zones between each of the stratigraphically adjacent cores are used to test lateral correlations in detail, scale the cores to one another, and combine them in a 4660-m-thick composite section. This composite shows that the entire post-Stockton sedimentary section consists of a hierarchy of sedimentary cycles, thought to be of Milankovitch climate cycle origin. Lithostratigraphic and magnetostratigraphic correlations between core overlap zones and outcrops demonstrate that the individual sedimentary cycles can be traced essentially basinwide. The agreement between the cyclostratigraphy and magnetostratigraphy shows both the cycles and the polarity boundaries to be isochronous horizons. Detailed analysis of the Newark basin shows that high-resolution cyclostratigraphy is possible in lacustrine, primarily red-bed rift sequences and provides a fine-scale framework for global correlations and an understanding of continental tropical climate change.Sedimentary geologypeo1, dvk2Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesMiocene stable isotopic stratigraphy and magnetostratigraphy of Buff Bay, Jamaicahttp://academiccommons.columbia.edu/catalog/ac:143455
Miller, Kenneth G.; Wright, James D.; Van Fossen, Mickey C.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12250Wed, 18 Jan 2012 00:00:00 +0000Previously reported biostratigraphic relationships from middle-upper Miocene sections exposed near Buff Bay, Jamaica (18°N, tropical bioprovince), differ from the subtropical North Atlantic (Sites 563 and 558). Time scales for this interval rely on correlations established at these subtropical sites, and the differences with the tropical section have implications to global correlations. Planktonic foraminiferal Zones N13 and N15 are thick at Buff Bay but are virtually absent at Sites 563 and 558; nannofossil Zone NN9 is associated with Zone N15 and uppermost Zone N14 at Buff Bay but is associated with Zone N16 at the other sites. Magnetostratigraphic data presented here further complicate the interpretation: Zone NN9 is associated with a thick normal magnetozone at Sites 563 and 558; at Buff Bay, it is associated with a thick reversed magnetozone. Although a secondary magnetization at Buff Bay makes it difficult to identify confidently Miocene normal magnetozones, the thick reversed magnetozone most likely represents the paleomagnetic field and correlates with Chron C5r. The magnetobiostratigraphic relationships require either diachrony of taxa or two mutually exclusive hiatuses in Jamaica and the North Atlantic. We address this problem by analyzing benthic foraminiferal δ18O and δ13C from the Buff Bay section. These isotopic data allow us to evaluate three hypotheses that reconcile the magneto-, bio-, and isotopic stratigraphic data and conclude that the first and last occurrences of five taxa were diachronous by ~0.3-0.5 m.y. between tropical and subtropical locations. This requires revised age estimates for late middle to early late Miocene biostratigraphic datum levels. We suggest that the ranges of several taxa are useful for endemic tropical or subtropical zonations, but correlations between the low and midlatitudes were affected by an increase in latitudinal thermal gradients during the late middle Miocene. However, we admit that further studies are needed before this issue is resolved.Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesPaleomagnetic results from the Silurian of the Yangtze paraplatformhttp://academiccommons.columbia.edu/catalog/ac:143391
Opdyke, Neil D.; Huang, K.; Xu, G.; Zhang, W. Y.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12235Tue, 17 Jan 2012 00:00:00 +0000Detailed sampling of two short magnetozones within the Matuyama Chronozone recorded at DSDP Site 609 (49.86°N, 335.77°E) confirms that one, the Cobb Mountain Subchronozone (1.12 Ma), is a very short, full normal polarity interval and that the other, the older interval, is a record of a geomagnetic excursion which occurred at approximately 1.55 Ma. The Cobb Mountain Subchron lasted approximately 25,000 years, one third the duration of the Jaramillo Subchron. The normal polarity interval is bounded by two transition zones which document an antisymmetry in the sequence of directions in the reverse to normal and normal to reverse polarity transitions. We interpret the antisymmetry as reflecting a dependence upon the sense of the reversal, without significant changes in the relative contributions of non-dipole terms. The polarity interval recorded at 1.55 Ma lasted only 8,800 years with what may be regarded as full polarity directions observed across only 3 cm of stratigraphic section. This feature is interpreted as an excursion of the geomagnetic field and appears to be correlative with the Gilsa Subchron. Similarities between the transition bounding these two magnetozones suggest that these features occur as the result of the same process or triggering mechanisms in the earth's outer core.Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesMagnetostratigraphy of a Lower-Middle Triassic boundary section from Chios (Greece)http://academiccommons.columbia.edu/catalog/ac:143372
Muttoni, Giovanni; Kent, Dennis V.; Gaetani, Mauriziohttp://hdl.handle.net/10022/AC:P:12229Tue, 17 Jan 2012 00:00:00 +0000The Marmarotrapeza Formation at Chios Island (northern Aegean Sea, Greece) is renowned for its Lower-Middle Triassic boundary sections in a marine Tethyan setting. Two sections have been sampled bed by bed to develop a magnetostratigraphic framework for the ammonoid and conodont biostratigraphy. The boundary sections occur within a lower normal (A+)-reverse (B−)-upper normal (C+) polarity sequence. The Lower-Middle Triassic boundary, placed at the first occurrence of the ammonoid genera Aegeiceras ugra Diener, Paracrochordiceras spp., Paradanubites depressus Fantini Sestini and Japonites sp., and close to the first appearance of the conodont species Gondolella timorensis Nogami, occurs in normal polarity zone Chios C+. The overall mean direction of the reversal-bearing characteristic component, whose early acquisition is suggested by a tilt test, is D = 271.2°, I = 33.2° (α95 = 11.7°, k = 112.5, N = 3). The inferred paleolatitude of the sampling sites is about 18°N, consistent with either an African or stable European affinity, although the declinations suggest large-scale counter-clockwise rotations with respect to Africa or stable Europe since the Early-Middle Triassic.Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesPaleomagnetic results of Tertiary sediments from Corsica: evidence of post-Eocene rotationhttp://academiccommons.columbia.edu/catalog/ac:143369
Vigliotti, L.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12228Tue, 17 Jan 2012 00:00:00 +0000Middle Eocene (Lutetian) and Lower to Middle Miocene (Burdigalian-Langhian) sediments from Corsica have been investigated in a paleomagnetic study to constrain the amount and timing of tectonic rotation of the Corsican block with respect to Sardinia and stable Eurasia. The sediments are generally characterized by weak and unstable magnetization, and only five Eocene and five Miocene sites out of 23 sites sampled provided interpretable data. Our best estimate for the Eocene paleomagnetic field for Corsica suggests ∼ 37° of counter-clockwise rotation, and no latitudinal change, with respect to stable Eurasia in post-Eocene time. This is similar to the amount of tectonic rotation documented from Oligo-Miocene volcanics from Sardinia, which is therefore consistent with Corsica and Sardinia being part of the same tectonic block since at least the early to middle Tertiary. Paleomagnetic results from the Miocene sites may represent remagnetizations but the presence of reversed polarity magnetization at three of the five accepted sites indicates acquisition before the late Pleistocene. The final rotation history of Corsica nevertheless is left unresolved.Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesWidespread late Mesozoic to Recent remagnetization of Paleozoic and lower Triassic sedimentary rocks from South Chinahttp://academiccommons.columbia.edu/catalog/ac:143387
Kent, Dennis V.; Zeng, Xiangshan; Wen, You Zhang; Opdyke, Neil D.http://hdl.handle.net/10022/AC:P:12234Tue, 17 Jan 2012 00:00:00 +0000Paleomagnetic results are described from eighteen formations sampled in the Nanjing (Jiangsu Province) and Yichang (Hubei Province) areas of South China. The marine platform carbonates and elastics range in age from early Cambrian to early Triassic. Progressive alternating field and/or thermal demagnetization analyses reveal predominantly single component magnetizations, sometimes of both normal and reverse polarity. These magnetizations, isolated in 457 of the 549 samples studied, typically have directions in geographic coordinates coincident with late Mesozoic to Recent fields. A secondary origin for the magnetizations is supported by negative fold tests in several units. A lower Carboniferous and possibly a lower Triassic limestone may have escaped the pervasive remagnetization; if the remanences isolated are indeed prefolding, a large counterclockwise tectonic rotation of the Nanjing area is implied by comparison with available Carboniferous and Triassic paleopoles reported from elsewhere in South China. This rotation may have been associated with Mesozoic left-lateral motion on the Tancheng-Lujiang fault zone.Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesA comparison of two sequential geomagnetic polarity transitions (upper Olduvai and lower Jaramillo) from the Southern Hemispherehttp://academiccommons.columbia.edu/catalog/ac:143366
Clement, Bradford M.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12227Tue, 17 Jan 2012 00:00:00 +0000Two normal to reverse (N to R) geomagnetic polarity transitions were obtained from a Southern Hemisphere deep-sea sediment core (35.91°S, 59.97°E). The upper Jaramillo reversal was continuously sampled by taking 0.5 cm thick samples across 55 cm of section, and the upper Olduvai reversal was sampled in a similar manner across 60 cm. Both records are characterized by full normal and reverse polarity directions which are in very good agreement with those predicted by axial dipole fields for the core site latitude. Each record also exhibits a zone yielding intermediate directions. Because of a large increase in both the within-level and the between-level scatter in the upper Jaramillo transition zone, it is not considered to represent an accurate record of the geomagnetic field. The upper Olduvai transition, however, appears to be a more coherent record. It is characterized by directions that shallow early in the reversal but then rapidly steepen to nearly vertical, upward directions. The declinations do not change until the inclinations have passed through the vertical. The total directional change occurs within a broad NRM intensity minimum. The virtual geomagnetic pole (VGP) path calculated for this record is not longitudinally constrained but instead exhibits a westward progression through the reversal. When considered together with the lower Jaramillo transition previously reported from this core, these records constitute a set of sequential Southern Hemisphere transitions. A number of striking similarities exist in the two records such as steep, upward directions and a shallowing which occurs between the near vertical and the full polarity directions. The results of zonal harmonic modeling of these records are consistent with the idea of a standing field which persisted across both the upper Olduvai and lower Jaramillo reversals.Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesEquatorial paleosecular variation of the geomagnetic field from 0 to 3 Ma lavas from the Galapagos Islandshttp://academiccommons.columbia.edu/catalog/ac:143378
Kent, Dennis V.; Wang, Huapei; Rochette, Pierrehttp://hdl.handle.net/10022/AC:P:12231Tue, 17 Jan 2012 00:00:00 +0000Complete progressive thermal demagnetization of nearly 400 oriented samples from 58 sites (lava flows) from the Galapagos Islands of Santa Cruz, San Cristobal and Floreana provide data for the statistical characterization of the time-averaged geomagnetic field near the Equator for the past few million years. Estimates of VGP dispersion due to paleosecular variation range from 9.2° to 11.8° depending on site selection criteria; our preferred estimate based on 64 site VGPs (51 accepted from this study and 13 from the 1971 study by Cox) is 11.4° (95% confidence interval 10.2–13.0°), consistent with previous estimates from the Galapagos Islands as well as paleosecular variation Model G, and confirming that angular dispersion of VGPs near the Equator is relatively low. The mean direction is not significantly different from a geocentric axial dipole field when account is taken of southward plate motion over the Galapagos hotspot. Preliminary paleointensity results from a comparison of the natural remanence with a total thermal remanence produced in a lab field of 15 μT on a subset of 321 samples from 48 sites that had relatively small changes in magnetic susceptibility after laboratory heating suggest that the time-averaged field was about 21 μT, or only two-thirds the present strength, in agreement with some other recent estimates.Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesRevised magnetostratigraphies confirm low sedimentation rates in Arctic Ocean coreshttp://academiccommons.columbia.edu/catalog/ac:143381
Witte, William K.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12232Tue, 17 Jan 2012 00:00:00 +0000The general lack of an age-diagnostic biostratigraphy in the Neogene sediments of the abyssal Arctic Ocean has emphasized the importance of magnetostratigraphy in providing chronostratigraphic control in these sediments. Sedimentation rates interpreted from early magnetostratigraphic studies of cores taken from the T3 ice island in the western Mendeleev Plain were estimated to be on the order of 1 mm/103 yr; however, recent amino acid epimerization studies of a core from the same area have suggested sedimentation rates of almost 15 mm/103 yr. This controversy has led us to reexamine the paleomagnetism of several of these cores. Our alternating field demagnetization studies indicate that many of these cores have an intense, high coercivity overprint, acquired after the core was opened, that is adequately removed only after treatment at 20 to 70 mT. We have remeasured samples from two cores after demagnetizations up to 80 mT and can confirm the position of the Brunhes/Matuyama boundary originally identified in the cores. In addition, the Jaramillo and Olduvai subchrons are identified. Average sedimentation rates in these two cores are 2–3 mm/103 yr, similar to the original estimates based on reversal stratigraphy, as well as those determined from recent radiocarbon studies, but incompatible with the amino acid-based dates.Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesTesting corrections for paleomagnetic inclination error in sedimentary rocks: A comparative approachhttp://academiccommons.columbia.edu/catalog/ac:143375
Tauxe, Lisa; Kodama, Kenneth P.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12230Tue, 17 Jan 2012 00:00:00 +0000Paleomagnetic inclinations in sedimentary formations are frequently suspected of being too shallow. Recognition and correction of shallow bias is therefore critical for paleogeographical reconstructions. This paper tests the reliability of the elongation/inclination (E/I) correction method in several ways. First we consider the E/I trends predicted by various PSV models. We explored the role of sample size on the reliability of the E/I estimates and found that for data sets smaller than ∼100–150, the results were less reliable. The Giant Gaussian Process-type paleosecular variation models were all constrained by paleomagnetic data from lava flows of the last five million years. Therefore, to test whether the method can be used in more ancient times, we compare model predictions of E/I trends with observations from five Large Igneous Provinces since the early Cretaceous (Yemen, Kerguelen, Faroe Islands, Deccan and Paraná basalts). All data are consistent at the 95% level of confidence with the E/I trends predicted by the paleosecular variation models. The Paraná data set also illustrated the effect of unrecognized tilting and combining data over a large latitudinal spread on the E/I estimates underscoring the necessity of adhering to the two principle assumptions of the method. Then we discuss the geological implications of various applications of the E/I method. In general the E/I corrected data are more consistent with data from contemporaneous lavas, with predictions from the well constrained synthetic apparent polar wander paths, and other geological constraints. Finally, we compare the E/I corrections with corrections from an entirely different method of inclination correction: the anisotropy of remanence method of Jackson et al. [Jackson, M.J., Banerjee, S.K., Marvin, J.A., Lu, R., Gruber, W., 1991. Detrital remanence, inclination errors and anhysteretic remanence anisotropy: quantitative model and experimental results. Geophys. J. Int. 104, 95–103] which relies on measurement of remanence and particle anisotropies of the sediments. In the two cases where a direct comparison can be made, the two methods give corrections that are consistent within error. In summary, it appears that the E/I method for recognizing and corrected the effects of sedimentary flattening is reasonably robust for at least the Mesozoic and Cenozoic when the source of scatter is geomagnetic and sedimentary flattening in origin.Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesIntegrated Anisian–Ladinian boundary chronologyhttp://academiccommons.columbia.edu/catalog/ac:143303
Muttoni, Giovanni; Nicora, Alda; Brack, Peter; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12210Fri, 13 Jan 2012 00:00:00 +0000We report magnetostratigraphic and biostratigraphic data from the Seceda core and the correlative outcrop section from the Dolomites of northern Italy. The Seceda rock succession consists of Tethyan marine limestones and radiometrically dated volcaniclastic layers of the Buchenstein Beds of Middle Triassic age (∼238–242 Ma). The Seceda outcrop section was correlated to coeval sections from the literature using magnetic polarity reversals and a selection of laterally traceable and isochronous lithostratigraphic marker beds. This allowed us to import the distribution of age-diagnostic conodonts, ammonoids, and daonellas from these sections into a Seceda reference stratigraphy for the construction of an integrated biochronology extending across a consistent portion of the Anisian–Ladinian boundary interval. Among the three options selected by the Subcommission for Triassic Stratigraphy to establish the Ladinian Global Stratigraphic Section and Point, we propose to adopt the level containing the base of the Curionii ammonoid Zone at Bagolino (Southern Alps, Italy) because this level is closely associated with a global means of correlation represented by the base of polarity submagnetozone SC2r.2r. The first occurrence of Neogondolella praehungarica in the Dolomites predates slightly the base of the Curionii Zone and can be used to approximate the Anisian–Ladinian boundary in the absence of ammonoids.Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesMid-Neogene Mediterranean marine-continental correlations: an alternative interpretationhttp://academiccommons.columbia.edu/catalog/ac:143300
Aguilar, Jean-Pierre; Berggren, William A.; Aubry, Marie-Pierre; Kent, Dennis V.; Clauzon, Georges; Benammi, Mouloud; Michaux, Jacqueshttp://hdl.handle.net/10022/AC:P:12209Fri, 13 Jan 2012 00:00:00 +0000Recent revised magnetostratigraphic and astrochronologic calibrations of several calcareous planktonic microfossil datum events (in particular Coccolithus miopelagicus and Neogloboquadrina acostaensis) combined with our magnetobiostratigraphic investigation of a 10 m-thick section at Ecotet, near Lyon (France), in which terrestrial micromammals (Vallesian Zone MN9) are intercalated with calcareous nannoplankton and planktonic foraminifera belonging to Zones NN6-NN8 and N14-15 (=M11 and M12), respectively, lead us to question the recent recalibration by Krijgsman et al. [(1996) Eart Planet. Sci. Lett. 142, 367-380) of the Aragonian/Vallesian (MN7-8/MN9) boundary with Chron C5r.1r (~11.1 Ma) and the lower/upper Vallesian (MN9/10) boundary with Chron C4Ar.2n (~9.6-9.7 Ma). Ecotet, with a uniform reverse polarity, is shown to be assignable uniquely to Chron C5r. Interregional correlation of Ecotet with Mediterranean terrestrial stratigraphies indicates that Progonomys (whose First Occurrence (FO) has been traditionally placed in Mediterranean Mammal Zone MN10) was already present in Mediterranean Zone MN9 at ~11.4 Ma and did not experience a 2 million-year delay in its putative prochoresis from Asia.Paleontology, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesMagnetostratigraphy and biostratigraphy of the Carnian/Norian boundary interval from the Pizzo Mondello section (Sicani Mountains, Sicily)http://academiccommons.columbia.edu/catalog/ac:143295
Muttoni, Giovanni; Kent, Dennis V.; Di Stefano, P.; Gullo, M.; Nicora, Alda; Tait, J.; Lowrie, Williamhttp://hdl.handle.net/10022/AC:P:12208Fri, 13 Jan 2012 00:00:00 +0000The 146.5 m-thick Upper Triassic limestone section at Pizzo Mondello in the Sicani Mountains of western Sicily is characterized by high quality of exposure, accessibility, and stratigraphic continuity. Magnetostratigraphic results delineate 12 normal and reverse polarity magnetozones, labelled successively from the base upwards as PM1n, PM1r, PM6n, PM6r. The Carnian/Norian boundary, based on conodont biostratigraphy, falls somewhere in the PM3n to PM5n interval which corresponds to the E14n to E16n magnetozone interval in the Newark reference sequence of polarity reversals. Comparison of magnetobiostratigraphic data from the Newark basin, Pizzo Mondello and other Late Triassic marine sections available from the literature suggests the existence of a reduction in sedimentation rate in the Tethyan marine domain at around the Carnian/Norian boundary. Although the Newark and the expanded Pizzo Mondello sections correlate well with each other, correlation with the condensed Kavur Tepe and Scheiblkogel sections is unsatisfactory. A re-interpretation of the Kavur Tepe results suggests that the section is younger than its previous correlation with the Newark section, and that it was deposited in the northern instead of the southern hemisphere. Most of the condensed Tethyan marine sections are seen to be highly discontinuous, as evidenced by concantenated conodont total range zones.Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesMilankovitch climate forcing in the tropics of Pangaea during the Late Triassichttp://academiccommons.columbia.edu/catalog/ac:143281
Olsen, Paul E.; Kent, Dennis V.http://hdl.handle.net/10022/AC:P:12205Fri, 13 Jan 2012 00:00:00 +0000During the Late Triassic, the Newark rift basin of Eastern North America was in the interior of tropical (2.5–9.5°N) Pangaea. Strikingly cyclical lacustrine rocks comprise most of the 6770 m of continuous core recovered from this basin by the Newark Basin Coring Project. Six of the seven drill cores (each from 800 to 1300 m long) from this project are used to construct a composite lake-level curve that provides a much needed record of long term variations in continental tropical climate. The correlations on which the composite section is based show complete agreement between lake level cycles and independent magnetic polarity boundary isochrons. The main proxy of lake level and hence climate used to construct this lake level curve is a classification of water-depth related sedimentary structures and fabrics called depth ranks. We then use Fourier frequency analysis (both FFT and multitaper methods) and joint time-frequency approaches to resolve the periodic properties of the cyclicity and the secular drift in those properties. A consistent hierarchy in frequencies of the lake level cycles is present throughout the Late Triassic (and earliest Jurassic) portions of the cores, an interval of about 22 m.y. Calibration of the sediment accumulation rate by a variety of methods shows that these thickness periodicities are consistent with an origin in changes in precipitation governed by celestial mechanics. The full range of precession-related periods of lake level change are present, including the two peaks of the ∼20,000 year cycle of climatic precession, the two peaks of the ∼100,000 year eccentricity cycle, the single peak of the 412,900 year eccentricity cycle, and the ∼2,000,000 year eccentricity cycle. There is also good correspondence in the details of the joint-time frequency properties of lake level cycles and astronomical predictions as well. Even in an ice-free world, the tropical climate of Pangaea responded strongly to astronomical forcing, suggesting that precession-dominated climatic forcing probably always has been a prominent feature of tropical climate.Paleoclimate science, Sedimentary geologypeo1, dvk2Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesA Late Triassic lake system in East Greenland: facies, depositional cycles and palaeoclimatehttp://academiccommons.columbia.edu/catalog/ac:143284
Clemmensen, Lars B.; Kent, Dennis V.; Jenkins, Farish A.http://hdl.handle.net/10022/AC:P:12206Fri, 13 Jan 2012 00:00:00 +0000The Upper Triassic Fleming Fjord Formation of the Jameson Land Basin in East Greenland contains a well-exposed succession, 200–300 m thick, of lake deposits. The Malmros Klint Member, 100–130 m thick, is composed of cyclically bedded intraformational conglomerates, red siltstones and fine-grained sandstones and disrupted dolomitic sediments (paleosols). The cyclicity is composite with cycles having mean thicknesses of (25), 5.9 and 1.6 m. The overlying Carlsberg Fjord beds of the Ørsted Dal Member, 80–115 m thick, are composed of structureless red mudstones rhythmically broken by thin greyish siltstones. This unit also has a composite cyclicity with cycles having mean thicknesses of 5.0 and 1.0 m. The uppermost Tait Bjerg Beds of the Ørsted Dal Member, 50–65 m thick, can be divided into two units. A lower unit is composed of cyclically bedded intraformational conglomerates or thin sandstones, red mudstones, greenish mudstones and yellowish marlstones. An upper unit is composed of relatively simple cycles of grey mudstones and yellowish marlstones. Recognized cycles have mean thicknesses of 5.6 and 1.6 m. The lake deposits contain evidence of seasonal, orbital and long-term climatic change. Seasonal change is documented by numerous desiccation surfaces especially in the Malmros Klint Member and Carlsberg Fjord beds, orbital change is suggested by the composite cyclicity, and long-term climatic change is indicated by the systematic upwards change in sedimentary characteristics of the lake deposits. The sedimentary features of the Malmros Klint Member suggest lacustrine deposition in a dry climate that fluctuated between desert and steppe conditions, the Carlsberg Fjord beds probably record lacustrine lake deposition in a rather constant dry (steppe) climate, while the Tait Bjerg Beds record lake sedimentation in a climate that fluctuated between dry (steppe) and warm moist temperate. In the Tait Bjerg Beds the upward change in cycle characteristics indicates a shift towards more humid conditions. Climatic deductions from sedimentary facies are in good agreement with climate maps of Laurasia, as simulated by numerical climate models. Palaeomagnetic data indicate a northward drift of East Greenland of about 10° from ca. 25°N to ca. 35°N in the Middle to Late Triassic. The Fleming Fjord Formation which represents ca. 5 m.y. of the Late Triassic interval was deposited during latitudinal drift of 1–2°. It is possible that the observed long-term upward shift in climatic indicators within the formation can be ascribed to plate drift, but southward shift of climatic belts could also have been of importance.Paleoclimate science, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesIntegrated Paleocene calcareous plankton magnetobiochronology and stable isotope stratigraphy: DSDP Site 384 (NW Atlantic Ocean)http://academiccommons.columbia.edu/catalog/ac:143292
Berggren, William A.; Aubry, Marie-Pierre; Van Fossen, Mickey C.; Kent, Dennis V.; Norris, R. D.; Quillévéré, F.http://hdl.handle.net/10022/AC:P:12207Fri, 13 Jan 2012 00:00:00 +0000At Deep Sea Drilling Site 384 (J-Anomaly Ridge, Grand Banks Continental Rise, NW Atlantic Ocean) Paleocene nannofossil chalks and oozes (∼70 m thick) are unconformably/disconformably underlain (∼168 m; upper Maastrichtian) and overlain (∼98.7 m; upper lower Eocene) by sediments of comparable lithologies. The chalks are more indurated in stratigraphically higher levels of the Paleocene reflecting increasing amounts of biosiliceous (radiolarians and diatoms) components. This site serves as an excellent location for an integrated calcareous and siliceous microfossil zonal stratigraphy and stable isotope stratigraphy. We report the results of a magnetostratigraphic study which, when incorporated with published magnetostratigraphic results, reveals an essentially complete magnetostratigraphic record spanning the interval from Magnetochron C31n (late Maastrichtian) to C25n (partim) (late Paleocene, Thanetian). Integrated magnetobiochronology and stable isotope stratigraphy support the interpretation of, and constrain the estimated duration of, a short hiatus (∼0.9 my) within the younger part of Chron C29r (including the K/P boundary) and an ∼6 my hiatus separating upper Paleocene (Magnetozone C25n) and upper lower Eocene (Magnetozone C22r) sediments. Some 30 planktonic foraminiferal datum levels [including the criteria used to denote the Paleocene planktonic foraminiferal (sub)tropical zonal scheme of Berggren and Miller, Micropaleontology 34 (4) (1988) 362–380 and Berggren et al., SEPM Spec. Publ. 54 (1995) 129–212, Geol. Soc. Am. Bull. 107 (11) (1995) 1272–1287], and nearly two dozen calcareous nannoplankton datum levels have been recognized and calibrated to the magnetochronology. Planktonic foraminiferal Subzones P4a and P4b of (upper Paleocene) Zone P4 are emended/redefined based on the discovery of a longer stratigraphic extension of Acarinina subsphaerica (into at last Magnetozone C25n). Stable isotope stratigraphies from benthic foraminifera and fine fraction (<38 μm) carbonate have been calibrated to the biochronology and magnetostratigraphy. A minimum in benthic foraminifer δ13C was reached near the Danian/Selandian boundary (within Chron C26r, planktonic foraminiferal Zone P3a and calcareous nannoplankton Zone NP4) and is followed by the rise to maximum δ13C values in the late Thanetian (near the base of C25n, in Zone P4c and NP9a, respectively) that can be used for global correlation in the Paleocene.Paleoclimate science, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesHigh resolution magnetostratigraphy of Caribbean Plio-Pleistocene deep-sea sedimentshttp://academiccommons.columbia.edu/catalog/ac:143278
Kent, Dennis V.; Spariosu, Dann J.http://hdl.handle.net/10022/AC:P:12204Fri, 13 Jan 2012 00:00:00 +0000The ability of the hydraulic piston corer (HPC) to recover virtually undisturbed sections of semi-consolidated deep-sea sediments suitable for paleomagnetic study was first demonstrated on Leg 64 and Leg 68 of the Glomar Challenger. Reported here is a complete magnetostratigraphy for a 150 m section of Plio-Pleistocene pelagic deposits recovered at Site 502 in the Caribbean. Correlation of the magnetic polarity zones to the well-dated standard sequence of geomagnetic polarity reversals provides a precise geochronological framework for age-calibration of calcareous plankton fossil datums and which, combined with the moderate to high sedimentation rates (24–38 m/m.y.), present an opportunity to study paleoenvironmental variations in the Early Pleistocene and the Pliocene with a time control and resolution heretofore possible only in Late Pleistocene deep-sea sediment cores.Physical oceanography, Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesSite 502: Colombia Basin, Western Caribbeanhttp://academiccommons.columbia.edu/catalog/ac:138504
Prell, Warren L.; Gardner, James V.; Adelseck, Charles; Blechschmidt, Gretchen; Fleet, Andrew; Keigwin, Lloyd; Kent, Dennis V.; Ledbetter, Michael T.; Mann, Ulrich; Mayer, Larry A.; Riedel, William R.; Sancetta, Constance; Spariosu, Dann J.; Zimmerman, Herman B.http://hdl.handle.net/10022/AC:P:11126Mon, 12 Sep 2011 00:00:00 +0000Our specific objective at Site 502 was to recover an undisturbed, complete section that could be used as a Neogene and Quaternary reference section. A complete record such as this would allow intercorrelations between (1) paleomagnetic stratigraphy, (2) calcareous biostratigraphy, (3) cyclic accumulation of sediment, (4) paleoceanographic changes, (5) oxygen and carbon isotope stratigraphies, (6) the chronology of Central American volcanism, (7) the timing and effects of the emergence of the Isthmus of Panama, and (8) the timing and effects of the initiation of Northern Hemisphere glaciation.Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticlesSite 503: Eastern Equatorial Pacifichttp://academiccommons.columbia.edu/catalog/ac:138507
Prell, Warren L.; Gardner, James V.; Adelseck, Charles; Blechschmidt, Gretchen; Fleet, Andrew; Keigwin, Lloyd; Kent, Dennis V.; Ledbetter, Michael T.; Mann, Ulrich; Mayer, Larry A.; Riedel, William R.; Sancetta, Constance; Spariosu, Dann J.; Zimmerman, Herman B.http://hdl.handle.net/10022/AC:P:11127Mon, 12 Sep 2011 00:00:00 +0000Our primary objective at Site 503 (Fig. 1) was to re- cover a complete, undisturbed Neogene and Quaternary section in the eastern equatorial Pacific. Site 503 is located near Site 83 in an area that contains an almost continuous pelagic record of the past 10 m.y. (Hays et al., 1972). Unfortunately, Site 83 was only spot-cored, and the recovered sediment is so badly disturbed by rotary drilling that most of the detailed record is lost. The section has an average sedimentation rate of 2.0 to 2.5 cm/k.y. with good-to-moderate preservation of all the major microfossil groups. We returned to Site 83 to core the same section, using the Hydraulic Piston Corer (HPC) to obtain an undisturbed, continuous section for high-resolution stratigraphic studies.Geophysics, Sedimentary geologydvk2Lamont-Doherty Earth ObservatoryArticles